Recovery teams are patrolling the streets of the Austrian capital in search of an increasingly rare breed of bright pink or blue bicycle.
Eight hundred of the three-gear machines, complete with grocery basket, were distributed in several central districts around the city just over a week ago.
However, the "Viennabike" programme, aimed at encouraging city slickers to propel themselves over short distances and then return the bikes, is going wrong. The chain locks at many of the specially built bike-stands are swaying idly in the wind.
After paying just €2 (about £1.25) to unlock a bike, many riders seem reluctant to hand it back.
This week a Hungarian coach was flagged down on the motorway after a tip-off to police that one of the bulky two-wheelers had been loaded into its luggage compartment.
The head of the company operating the bicycle scheme, Michael Kuhn, says several hundred calls a day to a hotline have also led to bikes being recovered from backyards, balconies, a roof-rack and the Danube canal.
But Mr Kuhn denies the developments have taken him by surprise.
"The only surprise," he says, "is the extent to which the Viennese are assisting with retrieving the bikes."Reuse content