Primary category is required even user shouldn't add posts to this category

Hi,

I have three categories:
Category X (Primary)
Category Y
Category Z

when I try to allow particular user group to add posts only to Category Z by editing ACL in category settings, I can't because he must to have on list Category X, because this category is Primary.

For users who don't have permission to add posts to Category X, EB should change and show Category Z as Primary, not Category X.
At now it force admins to allow adding posts to Primary category as required...

I'll be very grateful for help with this thread!
Best regards!
Adam