From Jean-Francois:

after spending a lot of time with numerous issues (most of them being my own mistakes). I could finally reach one point where I reduced the number of failures to "almost 0".

Why almost 0? Because I still get sporadically a problem which seems related to FEST (although I could never observe it before on Windows XP, it has occurred a couple of times with Vista 64 bits):
sometimes ScreenshotTaker.takeScreenshotOf() takes a snapshot of the panel but the screenshot contains no component at all! It looks like the screenshot was taken before the panel and its children were completely painted; after checking FEST source code (I'm still using 1.0 for the moment, I didn't want to add another potential source of tests mismatches to my current problems), it seems to me that screenshots are taken outside of the EDT and independently of any pending repaints. Can you confirm that this is intentional?
On my side I'll try if I can reproduce this problem systematically, but I'm afraid it's not possible.