Thanks for your help, i tried your suggestions but none of them worked...
Now to add to the weirdness, i found another messy album (still a flac rip), which is fine when tracks are sorted in decreasing order (23 22 21 20 19 ... 3 2 1) but wrong on increasing order
(20 21 22 23 1 2 3 4.. 19)...
I looked at the other messy albums and indeed decreasing order is never the reverse of the increasing order for those. I've made these tests with a sort only on "track number" (this was the only column with the sorting arrow).