It is not possible to delete a single blueprint from a difficulty/faction combination in the Wave AI manager.
How to reproduce:
- Open Wave AI manager
- click "add".
- add 2 blueprints for the comabination faction -1 and difficulty 1 and click "ok".
- click "edit" for this combination.
- click "del" for 1 blueprint. The blueprint will disappear. Then click "ok".
- click "edit" for the same combination. The combination still contains 2 blueprints.