I switched to FB 1.5, now the memory consumption maxes out at around 120 MB. So I played a little
with buffer pages, this does not seem to have too much of an effect. When going down to 512 pages
from 4096, it maxes out at about 80 MB, which is still very much since it stays there like forever.

I'll stick with Jason's advice and make an unprepare after having used LoadFromFile or SafeToFile.

Thank you all for your help

Florian