The cause for this problem lies in missing state-transitions of the interaction state-machine. DisplayConfigPACS.xml defines the events based on which the state-machine in DisplayInteraction.xml acts. For modifier-based interactions, a MousePressEvent / MouseReleaseEvent in combination with a modifier-key are responsible to transition into / out of the corresponding state ("move", "zoom", ...). When the modifier-key is released BEFORE releasing the mouse button, the second event is never triggered, causing the state machine to get stuck in that specific state, which blocks most other interactions.

There are two options I can think of right now:

1. Add new events for these specific interactions (i.e. "KeyReleaseEvent" in combination with a pressed Mouse Button) to catch both cases, first releasing the mouse button or first releasing the modifier key. This is somewhat complicated, as nothing in the direction of a "KeyReleaseEvent" is currently available and would need to be introduced by expanding how interaction of key events is handled.
2. Introduce a "catch all" event that resets any state back to default, e.g. by using a MouseMoveEvent with no additional keys pressed.