Converting a villager into a witch does not close the trading GUI

Steps to reproduce:

1. Summon a villager and give him a job.
2. Build a command block setup so you can summon lightning on the villager (with delay so you have time to open his trading GUI).
3. Activate the setup.
4. Open the GUI.
5. After the villager has been converted to a witch, the trading GUI stays open and you can actively trade in it.