I've had this issue over the last several iTunes releases, it loses focus when doing tag editing and is very annoying. I've reinstalled and set its properties to run in Windows 7 mode, no difference. No other program seems to be stealing focus, it's like iTunes just gives it up to nothing in particular.
My guess is probably the iPhone WiFi Syncing stealing focus. That is not the most stable process if you ask me, especially with multiple iPhones on the network.
Have you tried disabling that and seeing if the focus remains where it should?
No wi-fi sync enabled, and not even connected. Also happens during smart playlist editing, not just Get Info.
Windows Control Panel doesn't reveal anything at the time focus is lost either, very strange (and annoying!). It's as if iTune needs a dose of Ritalin ...