Thanks.
I added some logging statements to HandMorph>>#generateKeyboardEvent: and they show that this method is not run at all for Ctrl-Tab keyDown events.
But it is run for Ctrl-Tab keyUp events, and it returns a keyEvent for those.
It does not look like there is a OS level shortcut override for Ctrl-Tab, since it works correctly, in Safari for example (switch tabs).
Could it be a bug in the VM? I am running the Pharo 4.0 release VM and image.
Can anyone else running MacOS can confirm that Ctrl-TAB works for them in Pharo?