Solidify thickness doesn't correspond to specified scale although scale of object is applied I have the same problems as described in this thread, but the object to which I'm trying to apply "solidify" to has it proportions all set to "1"

What is causing this ?
Immediately after posting this question, I realised my problem.
Hopefully it might help someone else, in the future (or in the past)

The object was parented to a dummy object (this project is full of it, I think I didn't import this drawing the right way), which wasn't scaled properly, affecting the scale of the child-object.

I remember now that it appeared strange to me that the object (a technical drawing of a MAN NG272 Public Transport Bus, wasn't scaled properly, 
but as an afterthought I think it was, but the empty (empties) wasn't (weren't).

So, instead of removing the dummy parents, I just scaled the whole drawing  to what I thought was right, hence a number of problems later on ...

So the actual solution was to remove the parent of the object, keeping the transform (Alt-P) and then re-apply the scale, after which the solidify parameter works as expected.