I finally managed to find the source of my misery: it was the dreaded
multiarch setup on Ubuntu, or some related mess I obviously got into
with several 32 bit libs on a 64 bit system. I cleaned it all up and now
I pass the quickcheck fine.
I found out by mounting the "root" image and trying to "chroot" to
it.
Then I checked the required libraries for "bash" and noticed that the
dynamic linker was missing.
Thanks again for your help.
Best
Oliver