To properly retrigger hold-taps when a combo is not activated, some
position down events are reraised instead of released. The corresponding
position up events were never reraised, causing a potential stuck key.
this makes LS(LEFT_CONTROL) work as if shift and control were both
pressed explicitly. Previously, the left shift would have been released
as soon as another key was pressed. The implicit behavior is useful in
case of LS(NUMBER_1) when rolling over to other keys.
Also see #361.
