Overijse stands beside the line which divides officially Flemish-speaking Flanders from officially bilingual Brussels (and is a dozen or so miles from officially French-speaking Wallonia). But the mainly French-speaking middle class of Brussels - like the middle class of every city - is increasingly tempted to move out to the green and leafy lanes of places such as Overijse.
Their arrival is driving up property prices and, more to the point in Belgium, threatening to swamp the town-cum-suburb's Flemish character and language. Local feelings are running so high that a Flemish MP has drafted legislation to allow specified Flemish communes to limit 'immigration' - not immigration by foreigners but immigration by other Belgians.
Of those wishing to settle in Overijse, and similar Flemish satellites of Brussels, priority would be given to those who speak Flemish or have a job in the town or historic family links with the commune.
For Flemings the issue is survival; they see nothing sinister in the proposal. For Walloons the issue is freedom of movement within their country; to them, the proposal smacks of apartheid. Emotions on either side have been stoked by inflammatory coverage in the French and Dutch language press. Here is another archetypically Belgian problem. How can a country know itself when there is no national media?
Greta, who serves in one of Overijse's mouth-watering bakeries, thinks the whole thing has gone too far. 'We (Flemings) all make an effort to learn French but the Walloons and the French nationals who come never bother to learn Flemish. It suggests they are not interested in integrating if they cannot be bothered to learn the language.' She turns to a woman who asks for a loaf of bread - in French.
The adoption of a new federal constitution in Belgium this year, which devolves greater power to the regions, has coincided with the 30th anniversary of the creation of the linguistic frontiers. The status of Brussels - a region in its own right - has always been controversial. As the city expands, to fulfil its European role, it is provoking a nationalist, or regionalist, backlash in its own backyard.
'It's not politics. I grew up here, I want my children to feel they belong here too. We speak Flemish at home and I don't want them to ever feel there is anything wrong with that,' said Maria, 40, who has lived in Overijse all her life.
Nowadays it is regional, not national, politics which attracts the Belgian political talent; the language question dominates and permeates all political questions. In Flanders, everything is further complicated by the emergence of the right-wing nationalist Vlaams Blok and associated militant groups such as the Taal Aktie Komitee, which uses nationalism as an excuse for criminal thuggery.
In this climate the proposed residency law in Overijse is a political time-bomb. First tabled three years ago it has been repeatedly thrown out, amended and re-tabled. At every stage it has been the subject of a legal challenge from the Walloons. The Prime Minister, Jean-Luc Dehaene, temporarliy defused the issue in July when he ordered the Constitutional Court to check whether, under the new constitution, the Flemish region was constitutionally competent to rule on such an issue. The court said it was not.
Re-amended and watered down to get round the objections, the proposal will be represented to the Flemish council this month. A rival Flemish socialist motion seeks to discourage the property speculation at the heart of the dispute. It proposes that if house prices in Flanders increase more than 10 per cent from a fixed level the commune will be allowed to buy property at a special price and sell it on cheaply to anyone who can demonstrate a social need to live locally.
But this will only exacerbate another Belgian problem - over-spending by national, regional and local authorities.