I’ve noticed two annoying things today that I didn’t notice before so I think that the system got corrupted or I must’ve changed some weird preference somewhere that I didn’t mean to:

1. If I Command-Tab repeatedly, maybe 1 out of 20 times, one of the icons is missing. For example, right now I’m running 5 apps: Finder, Thunderbird, Firefox, Terminal, and Adium. Maybe one out of 20 times, one of them is missing – most often the missing one is Thunderbird but I’ve seen Terminal and Finder disappear too.
2. Also, it appears that my Mac will only show one application at a time, which is not the way I remember it working before today. For example, if I am in Adium and then Command-Tab to something else or click on the Desktop, then Adium disappears. It used to stay running tucked away nicely on my PowerBook screen while I worked on my external monitor, but now it keeps disappearing. I confirmed with a coworker, also with a PowerBook running 10.4.2, that this doesn’t happen for him. It’s not just Adium. Every app is doing this. There’s also something weird going on where the Hide command is grayed out and Command-H doesn’t work. I can temporarily resolve this with a Show All but that only works temporarily.

Any ideas?

Update 2005-07-30: I posted last night to the macosxhints forums and now that my post has been approved, here’s the link.
No stunning reveleations yet – maybe it’s time for a trip to the Genius Bar…

Update 2005-07-30 1:53 PM PST: Taking the advice of jbc @ macosxhints, I looked in the Activity Monitor. Nothing unusual there, except that it reminded me that I am running Quicksilver (B42) and then I wondered if it could be Quicksilver related. I quit Quicksilver and the problem went away. Then I remembered that I had, uhhh, messed around with some Quicksilver options the other day to see what they did… 🙂 The culprit was in the Extras tab and it’s called “Hide other applications when switching (shift prevents)”. I think when I checked it, I had assumed that it only applied to switching apps using Quicksilver – didn’t realize that it applied to Command+Tab switching too. Anyways, I disabled that and now it seems like both problems are gone – knock wood.

Thanks!