The mentions dropdown does not handle input containing space well

The user dropdown for @mentions does not work well when a space is inserted while querying for users. E.g. for input 'Xavier Sa' on JAC 3 positions were displayed, but when pressing arrow down to pick second position, the event was not captured by the dropdown, and resulted in the default behaviour - caret moving to the next line (or end of the current line if it was the last one).