What was causing this on mine was the small anti roll bar bracket which attaches to the dog bone on the front height corrector. The bar that comes off it that the dog bone connects to was deformed and bent so not in its true position. This was the cause!
The solution....a new bracket costing £24 all in from Citroen. Once fitted, which took my mechanic literally 5 minutes, the ride height was back correct again and the front end no longer rises or drops when turning
An amazing result for me as its such a change to the cars driveability and such a simple and cheap fix.... a welcome change on a hydraulic Citroen