That sound like a Mac problem on Windows Alt+Tab your Option+Tab is used to switch application. If a ScriptUI Dialog is open in Photoshop I can use Alt+Tab to switch from Photoshop to for example switch to Chrome and in Chrome I can use Crtl+Tab to switch Chrome's tabs. That would be CMD+Tab on a Mac. So it looks like ON Windows Ctrl+Tab get passed to the current application where Atl+Tab your Option+Tab is an OS shortcut windows has for switching applications. In Photoshop with a ScriptUI dialog open Crtl+Tab (CMD+Tab) does nothing... The solution is to run Windows on your Mac.
Haha, that sounds like an extreme solution to a problem this size!
I can Cmd+Tab just fine when the dialog is up and doing nothing, but it's only when it's in the middle of processing that it stays on the screen when I swatch applications.
I do not know how Mac OSX hadles runing task a active windows and window focus Perhaps the running process is stealing systen window focus from OSX CMD+Tab feature and the ScriptUI dialog window gets focus. It may be OSX is handling contention for systen Window focus.