I've noticed it only happens whenever I have the window stretched to be widescreen. The wider the window is, the less I can zoom out. This is weird because I played the first 6 levels yesterday full screen at the same res, and this didn't happen
EDIT: Very weird, I just reactivated FS after playing 2 levels windowed and it's fixed... The bug WAS there, no idea why tough... Well I'll post if it happens again, thanks.