Found a small bug with Qualifiers, tested in Event Behaviours. The qualifier of another object will disappear after editing an action if the qualifier has no actions, and it cannot be added back in until close and re-open the behaviour editor.
Steps to reproduce:
1. Create two active objects.
2. Create an event behaviour on the first.
3. Add the Neutral qualifier on the second.
4. Open the event behaviour of the first and create an event with an action to set alterable value to 0.
5. Using the event headings (import new objects), bring in the Neutral qualifier but don't add any actions to it.
6. Edit the Set alterable value action then click OK.
7. The Neutral qualifier has disappeared and cannot be added back in (until window is closed and opened again)