Product changes don't take effect (1.4.2.5)

[4140]

For a few days now I have a strange problem. When making changes to product in BO, after saving I get the affirmative message that the changes have been saved. When I check, however, the old information is still active.

The first time I had this problem it was gone after a few hours and I thought it was a short problem with my server. But now the problem is back and I can't figure what could be the cause.

It can't be file and folder permissions, b/c I haven't changed any and I checked with another working installation if there were differences, but i didn't find any.

The only reason left is some problem with Prestashop and I can't figure out what it could be.

Tried switching to 1.4.3, but it didn't fix this issue and I'm back with 1.4.2.5 now.

Please help