I see this topic is 4 yrs old, but I just recently ran into this while trying to takeover my first new room. The link to the changelog is no longer valid in Dissi's post.
Is there somewhere that this is documented?? This was super frustrating trying to figure out the difference between 'attackController' and 'claimController'.
Also the game popped up this tip which makes no mention of the 5 CLAIM parts rule. This tip appears to no longer be true?
From what I can tell the current behavior is: If controller is unowned, then use claimController If controller is owned, then you may use attackController (but only once every 1000 ticks).