Thanks for your help! This list is so incredibly quick.
I asked this question here on the list only as a last resort because I have been searching for the bug for over a week now. Just this minute I found the bug. It is not in Maxima. It was a 1 entry where a 0 should have been. Hidden deep down :-(
Good to know simp:false anyway :-)
One can consider that as solved now...
Best regards,
weaker