Ok or not ok?

*#reposted from parenting & family#*

My husband's ex has been being difficult since they're in process of getting the existing contact agreement legal via court (she wanted it not legally changed because then she could just turn back whenever she wanted)

That's only partially relevant here..

So last week (may 22nd to be exact) their son (14) missed yet another deadline for school, he's been slacking a lot so I agree a punishment would be in place.

However, she took advantage of her possibility of turning back the custody agreement since my husband tried making it legal and he now has them 4 days every other week (fri to tue) in stead of 50/50 which it was before.

... Actual issue:

So she punished the kid by saying that he needed to do a book report for her in my husband's weekend (may 30th-june 2nd, more than a week after the missed assignment deadline)

He severely feels that if she wants to punish their kid, she should not be doing it in his time with the kids, or at least have a mutual agreement about a punishment if it needs to cross over to the other parent.

What are your thoughts?