The Socialist Party's convention was dominated by expressions of outrage, and newspaper commentators were moved to ask awkward questions not just about the mayor of Paris, but about the power wielded by the capital's Gaullist establishment and about the French justice system.
The court's decision, announced as the first wave of urban holidaymakers was en route to the south, related to specific accusations that a flat owned by Paris city council had been expensively altered and refitted before being occupied, at a subsidised rent, by Mr Tiberi's son, Dominique.
Tiberi junior's flat - a penthouse in a fashionable quarter of the city - had been the talk of Paris ever since a former deputy head of the city housing department, Francois Ciolina, had testified that more than 1,500,000 francs (pounds 190,000) of council money had been used for the refurbishment. He also said that Dominique's mother had personally overseen the work.
Although Mr and Mrs Tiberi denied the allegations, noting that Mr Ciolina was himself under investigation for corruption, the affair rumbled on. Mr Ciolina offered documents. An inquiry was opened by judge Eric Halphen, who was already investigating corrupt contracting in the Paris housing department.
Within a few days, it was reported that the case of the Tiberi flat was being switched to a judge in central Paris, on the grounds that this is where the offence had allegedly taken place. The reason why Judge Halphen had taken on the case was that the refurbishment of the Tiberi flat was carried out by the firm at the centre of the general housing corruption probe and this firm is registered in the judge's jurisdiction.
Judge Halphen has a reputation as an anti-corruption campaigner and for not being easily intimidated - qualities which explain why he instituted both cases and why, many suspect, the Tiberi case was suddenly removed from him.
Within hours of formally taking over the case, the new judge announced that the case was being dropped on two technicalities: that the allocation of city council flats to the Tiberi children had been investigated and dropped last year, and that the refurbishment took place more than three years ago.
Mr Tiberi, who had a rocky first year as mayor of Paris, taking over from Jacques Chirac, hopes that the affair is now closed as successfully as was the affair of the prime minister's subsidised housing when he agreed to move out before Christmas. This time the clamour may not die down so easily.
Those implicated now include the justice minister, Jacques Toubon, who reallocated the Tiberi case, other senior Gaullists on the city council, and even Mr Chirac, who as mayor for two decades presided over a system of patronage that looks increasingly suspect.