First they "stole" an Indonesian folk song. Then a sacred temple dance. Now Malaysians are being accused of appropriating batik, the traditional dyeing technique, sparking violent demonstrations in Indonesia and top-level meetings to defuse growing tensions between the two neighbours.
Batik was recently recognised by the UN's cultural body, Unesco, as part of Indonesia's distinctive heritage. The country's President, Susilo Bambang Yudhoyono, who is frequently seen in elegant silk batik shirts, has urged all his compatriots to wear batik this Friday, in celebration. But Malaysia still claims the technique as its own.
And thanks to this and other disputes, relations between the two Asia-Pacific rivals are at their lowest ebb since the pair fought an undeclared war over the island of Borneo in the 1960s.
This month, there have been ugly scenes in Jakarta, where gangs of youths armed with bamboo spears stopped cars and demanded motorists' identity cards, in a hunt for Malaysians. Indonesian protesters also pelted the Malaysian embassy with rocks and rotten eggs, and burnt their neighbour's national flag.
Malaysia expressed concern about the safety of its citizens working and living in Indonesia, prompting emergency talks in between the Indonesian Foreign Minister, Hassan Wirajuda, and his Malaysian counterpart, Anifah Aman.
Malaysia's alleged theft of cultural traditions to which Indonesians claim ownership has wounded the latter's national pride. The two peoples have much in common, including a similar language and ethnic roots; but, like over-familiar siblings, they are often at odds. Indonesians recently claimed, for instance, that the Malaysian national anthem is a rip-off of a song written in their country in the 1950s.
The plagiarism charges were repeated when Malaysia used an Indonesian folk song, "Rasa Sayang", or "Feelings of Love", in its "Malaysia, Truly Asia" overseas tourism campaign. And Indonesian anger was compounded by an advertisement on the Discovery Channel for a documentary series about Malaysia featured a Balinese ritual temple dance known as the pendet.
Indonesians rejoiced, then, when Unesco announced that it was recognising batik as theirs, Aburizal Bakrie, the co-ordinating minister for the people's welfare, gave a speech stressing how important batik was to Indonesians. It contained "symbols and a deep philosophy of the human life cycle", he said, describing it as "a cultural icon with its own uniqueness".
Malaysia begs to disagree, pointing out that it, too, has vibrant batik centres, producing shirts and sarongs decorated with patterns created in the traditional manner, using wax-resistant dyes. To that, Indonesia retorts that Malaysia is poaching its artisans.
The Indonesian news magazine Tempo reported last week that many batik craftsmen had moved to Malaysia, tempted by offers of good wages and a secure future for their families in a country with significantly higher living standards. There are also claims that Malaysian businessmen are buying half-finished batik from markets in Indonesia, then adding the final touches back home before marketing the items as "Made in Malaysia". Such issues might seem trivial, but they are helping to whip up an aggressive nationalism not seen the so-called "Konfrontasi", when Indonesia's founding president, Sukarno, declared a policy of confrontation aimed at destabilising the newly created Federation of Malaysia. A guerrilla war against Malaysia's territories in Borneo, launched in 1963, was unsuccessful and led to Sukarno's downfall three years later.
Forty years on, the two countries are still sparring, over territorial and diplomatic issues as well as cultural matters. This year, the Indonesian Navy chased a Malaysian warship out of disputed waters in the oil-rich area of Ambalat. Not far off, lie several long-contested islands which an international court decreed in 2002 belong to Malaysia, much to Indonesia's chagrin. Tempers have also flared over the treatment of migrant workers in Malaysia, following several well-publicised cases of Indonesian maids being badly abused by their employers. The Indonesian government imposed a ban on women travelling to Malaysia to undertake such work, which has yet to be lifted.
Then there is the sensational case of an Indonesian teenage model, Manohara Odelia Pinot, who has accused her husband, a Malaysian prince, of kidnapping, raping and torturing her. The story long dominated the headlines in Indonesia, with Ms Pinot – who made a midnight dash for freedom during a visit to Singapore – claiming that Tengku Temenggong Mohammad Fakry treated her as a sex slave, something he has denied.
Some commentators say the nationalistic rivalries are absurd, pointing out that borders were fluid in pre-colonial times and people moved around the region, leaving behind their languages, religions and cultures.
But relations between Malaysia and Indonesia deteriorated so badly this year that the former's Defence Minister, Ahmad Zahid Hamidi, felt obliged to deny publicly that they were on the brink of war. Now tensions have soared again, thanks to batik.
Muchtar Bonaventura, leader of the Bendera vigilante group, which mounted the roadblocks and protests in the Indonesian capital, told the Jakarta Globe: "Malaysia has stolen from us and insulted Indonesia. We feel offended and angry."
The latest row, according to Indonesia, follows a series of claims by Malaysia to Indonesian artistic and gastronomic traditions. They include gamelan, the traditional Balinese percussion instrument, and rendang, a dish of meat simmered in spices and coconut milk. Some Indonesians call their neighbour Maling-sia. In Indonesian, maling means thief.
After the foreign ministers' meeting in Jakarta, Mr Wirajuda said that he and Mr Anifah had agreed to avoid "sensitive issues" such as staking claims to each other's cultures.
But Indonesia is already gearing up for the next battle. A few years ago, it persuaded Unesco to acknowledge wayang (traditional shadow puppetry) and keris (a ceremonial dagger) as distinctly Indonesian. Both had been claimed by Malaysia. Now the two countries are exchanging vitriol about angklung, a bamboo percussion pipe which Indonesia says originated in West Java.
"We will keep fighting for our heritage one tradition at a time," declared Jero Wacik, Indonesia's Culture and Tourism Minister.
Indonesia: Bigger but poorer
*Population: Indonesia is the world's fourth most populous nation with 234.3 million people. Malaysia is nearly ten times less populated, with just 27 million
*Size: Indonesia is made up of more than 17,500 islands, covering a total of three-quarters of a million miles; Malaysia's territory spans a third of this area.
*Malaysians are generally expected to outlive their neighbours. The average life expectancy is 72 years for men, compared to Indonesia's 68, and 77 for women, compared to Indonesia's 73.
*Malaysia is also a richer nation. Its GDP per capita is $6,956, the third-largest in the region and almost seven times that of Indonesia, which is just $1,025.