hmm. It seems to be set to the key under escape. Wonder why...
Someone set the machine to "English" not "Real English"
Time for a cup of tea I think.
Try going to Preferences>General and uncheck Use System Keyboard Shortcuts (or something like that).
That's NEVER on.
Have tried International Prefs and Keyboard shortcut prefs.
I now think it is a Mac Wide rather than anAE thing, I just hoped someone had found it.
Tilde switched for Backtick somehow.
Have replaced Keyborad shortcut prefs with fresh ones and it wasn't that so must be an OS thing.