Since upgrading to Lightroom 5 (I'm using 5.5 now), I've had all sorts of weird behavior and slow performance, particularly in the Library module. After heavy use in the Library, Lightroom starts to refuse to reorder, or add to collections, or it will open the wrong photo in Photoshop when I press Ctrl-E, all kinds of things. One day I couldn't quit by pressing Ctrl-Q; it would bring up the Export dialog box. Typically if I exit and restart, the problems go away for a time.
Today, the latest is this:
I've deleted the Preference files once, and I regularly optimize the catalog. Any clues where I could go from here?