[wp-testers] What makes themes corrupted?

[Tassoman (mailing)]

After last svn update, I was editing themes by online admin pages
editor. Then i got my personal theme corrupted and WP reverting to
default.

For now I've moved default to default2 and moved mytheme to default and
WP is (dirty) working as ever. 

But what makes a WP theme a corrupted WP theme? I'm missing something?
Or I'm talking about some bug?