Shortcuts that are a combination (f+i) are saved under the second key - if there is a collision in that second key, the callbacks can misfire

[milemons]

Example:
I have two shortcuts: i which will navigate my page and f+i which will add a new item to the page.
If I just press i while selected on an item on the page, it will match with the f+i shortcut because that is saved under the self._callbacks[i] even though it is a combination.

[Persola]

See #323