I raised the car to its highest position so that I could free the rear suspension strut spheres.
For safety I put a wheel ramp under the metal 'box' surrounding each rear strut.
There was a gap of approximately 1 cm.
I put wood supports under the front of the car, again with a 3cm gap.

After freeing the spheres I lowered the car so that it rested on the supports.
I de-pressurised the system, changed the spheres and raised the suspension.

However the rear was still resting on the wheel ramps. I tried all the height positions, turning off the engine, bouncing the car and even pulling on the height corrector linkage. nothing worked.
The weight on the ramps was at its minimum when the height was in normal ride mode.

I had to use bottle jacks to raise the chassis and pull out the trapped wheel ramps.
This also happened on the previous occasion that I tried this method.

Why did the suspension not go back to the original height?
What was I doing wrong?

It would appear that the height sensor thinks that the car is to low and is trying to raise it, why that would be I don't know but you can try detaching the link to check that the corrector is working.

Peter

Leaving the wheels hanging would of left the Rear Height Corrector on the full HIGH position, so the system assumed the car was in the high setting and so didnt need to add fluid..

The way I do it is with a trolly jack, and an axle stand. The jack is placed under the same place you had the ramps, then when on high the stand is used as safety to hold the car up in the event of failiure.. then after the spheres are "Cracked", remove the stand, set on low setting, and lower with the jack.. after all fuild is returnd, jack the car back up, refit stand, swap spheres, remove stand, and lower jack. Tighten 12mm pressure regulator, start engine.. let the car come up off the jack.