A very likely cause is malfunction of the computer within the stalk switch assembly (known as COMM 2000). Electrical malfunctions of wipers/indicators/lights seem to be very common on 'electronic' Puegeot and Citroen vehicles; there are a number of forums on the web where such issues are questioned and discussed. It is more than likely the Comms 2000 would need to be replaced - which is expensive!!
Boot
November 2009