About two weeks ago my Win7 (32-bit) system developed a hugely annoying behavior. When the standard, new "Save as" or "Open" dialog box pops up and closes, the application which opened it freezes for 8-10 seconds, and the open or save operation that the dialog is used for is only completed after the app comes out of the freeze.
Strangely enough, the freeze happens even if the dialog box is canceled, so it seems to be related to the internals of the dialog itself, not to whatever the application does with it.
It doesn't always happen, but often enough to be a big nuisance. Maybe 30-50% of the time, but seemingly at random. Let's say I have 10 tabs opened in Firefox. I go from one tab to another and press Ctrl+S in each to save the HTML document. The freeze will happen for about half of the tabs, but sometimes for all of them. Each time the file gets saved only after Firefox unfreezes.
At first I thought it was a Firefox problem, but no, the freeze occurs in any app that uses the modern Save/Open dialogs in Win7. MS Office apps have their own dialogs, and they're immune. Some old apps stick to the Windows 95-style dialogs, and they're immune too. Only apps that use the latest incarnation of the dialogs get frozen.
I removed everything I have installed recently, removed my machine from the homegroup, tried Autoruns and friends, everything I could think of. I was this close to restoring the system image from a month ago.
Finally I tried disabling the real-time protection in MSSE, and it seems to have helped. I've been running a whole day without a single freeze, so I'm pretty convinced MSSE is responsible, though I can't see how it could be (what in MSSE could freeze the app after the dialog has been CANCELED and no files were accessed at all?).
It seems to have started under two weeks ago, but I can't pinpoint it any better. I did install SP1 more or less at that time, so there's another suspect, although that wouldn't account for why the problem goes away if I disable a part of MSSE, and I think I would have noticed if the freezes started occurring immediately after installing SP1. Has anyone else seen anything similar?