I don’t know. With the preferences, it is usually not an actual preference itself that can be changed back to fix it. It is usually a corrupted prefs file. However, it is strange that it was multiple computers. Maybe the corrupted file was propgated across all of them.
Anyway, it you don see it come back after changing a setting then let me know. There are no settings I can think of that would cause it. But if you find one that does then let me know.