automagical jumping to the Default Theme

Hi,

I’m having very strange problem :/

I just want to change my blog theme, and I’ve tried to use different themes but after some time my blog is automagically jumping to the Default Theme. I don’t know why this happens :/ I’ve tried with several themes and the same problem remains.

I select a theme, which is different than a Default Theme, and at the first minutes I can see my blog using the selected theme, but after a minute or so it’s using Default Theme… it’s jumping to Default Theme…

Interesting point is that when I remove the Default Theme, I can’t see my blog, it’s showing a white blank page. When I go to Design section in Admin panel, no template is selected.

Does it mean that WP 2.5 RC2 doesn’t use themes except Default Theme?

What could be the problem here, please help me.