I have spent some time fully dismantling two "faulty" rear locks and have devised a guaranteed method of unlocking a rear door from the inside. Once the door card is removed my method takes less than 10mins and uses only a soldering iron and instrument screwdriver. The door and lock remain undamaged and useable.
Please see the attached PDF CITROEN C5 - Opening an unopenable rear door PDF.pdf 902.16KB 8 downloads.
I can provide my more detailed analysis of the lock if anyone wants it.