Simple fix. Somewhere in your key bindings there is a command that is bound to Option+7. Go to the Tools > Options dialog, and in the Keyboard and Mouse section, go to the Key Bindings page.
In the "Search by key sequence:" field, type the Option+7 (Pipe) key, and you'll see the text "Option+7" show up in that key sequence field. Below it you'll see the list of commands bound to that key, which I'm guessing will be several instances of "activate-call-stack". Highlight each entry and use the "Remove" button to remove that binding.