Disappearing footage

I've come across an odd issue with Premiere Pro CS5.5. It hasn't caused any major issues, but I'd like to see if I can fix it.

On larger projects, footage in my Project window (sometimes when grouped into bins, sometimes not) disappears...but clips taken from that footage stay in their proper place on the timeline, and run just fine. This mainly seems to happen with a large number of items in the Project window.

Has anyone else experienced this? Any ideas what might be causing it?

Thanks,
Brian

Thanks, Vince. Nope, the search box is totally empty. When this started happening, I reverted back to an earlier version of the same project I was working on (in which everything still appeared)...but within a day, the same thing started happening with it.

I'm wondering if this is one of those "uninstall/reinstall" problems...

Brian