[Plugin: NextGEN Gallery] Thickbox effect lets menu bar shine through…

I′m using the latest wordpress+the latest nextgen gallery. I′ve been using the same on a different site, with the fusion theme, and now I tried it on the Smoky theme.
It was working fine, till suddenly the images let the main menu “shine” through when clicking on them. Any idea on what could′ve happend?
Kjersti