Changing the action type for new actions resets the fields but not the begin date completely

When I go to the page to add a new (platform) action, I can select Platform Application, and set there the start date, the description and the contact as this:

When I then change the type to Platform Observation all the fields are reset - except the start date (I haven't tested the end date, but I expect a similar behaviour).

When I then rely on the start date that is shown - and just set the description and the contact, I'm not able to save the action:

This is because the start date for the form still seems to be set (with the old value), but it is not set in the entity that is send to the server (not null constraint).

(Same happens for generic device actions),