September 13th, 2006 • 9:44 am
After some further testing on my semi-dead G5 Quad, I have finally been able to discover what appears to be causing the bug with fast user switching in Mac OS X 10.4.x, which triggers a color/brightness shift and causes the “Color” tab of the “Displays” preference pane to cease to work properly.
I managed to identify the source of the problem by removing my entire “Preferences” folder inside my home library folder, and then restoring the preference files bit by bit. Removing the entire “Preferences” folder eliminates the problem. In other words, if you are a Mac OS X 10.4 user experiencing the bug with fast user switching, if you drag your entire “Preferences” folder from your home library folder to your desktop, then log out, then log back in, and then use fast user switching, the color shift and “Displays” failure will no longer happen.
If, however, you move all your preference files back inside your “Preferences” folder inside your home library folder, then the problem reappears.
So clearly, the problem is with one of the preference files. But which one? By restoring my preference files in batches, It didn’t take me too long to find the culprit: It’s the file called “com.apple.systemuiserver.plist.” If you just remove that file from your “Preferences” folder inside your home library folder, then log out and log back in and then try to use fast user switching, you’ll notice that the color shift and “Displays” failure no longer occur.
If you restore that “com.apple.systemuiserver.plist,” log out and log back in, the problem will reoccur. And it will reoccur even on a machine with a single monitor. It doesn’t require a dual-monitor set-up. And I am also pretty sure that it doesn’t require the use of customized color profiles. (I was also able to reproduce the bug on a MacBook with the default color profile.)
I was actually able to narrow the source of the bug down even further. All you need to do in order to make the problem reoccur (at least on my system) is to check the option labelled “Show input menu in menu bar” in the “Input Menu” tab of the “International” preference pane.
I found this out because I knew that the “com.apple.systemuiserver.plist” preference file contains settings involving the “International” preference pane. And I knew that because I am a long-time Spell Catcher X user, and Spell Catcher X works through that input menu.
So effectively in order to avoid the bug with displays and fast user switching, you need to not use the input menu. Sadly, for Spell Catcher X users, this is not an option. We have to use the input menu, because that’s how Spell Catcher X’s features can be accessed. I was also able to verify that Spell Catcher does run with the input menu hidden, but the bug with displays and fast user switching still occurs when the input method is Spell Catcher, even if the input menu is hidden.
In other words, in order to avoid the bug, you have to avoid using Spell Catcher altogether, and keep the input menu invisible. I am afraid this is not an option for me, so all I can do is report my findings to Apple and hope that they fill fix the bug in a future system update. But maybe there are other Mac users out there affected by the bug who are not Spell Catcher users and who just happen to have the input menu visible in their menu bar. For them, hiding the input menu will be enough to eliminate the bug.