Unable to free an IP

I need to free some IPs from our CP but with two specific domains inside a reseller it's impossible to do it.
From the "manage IP's of the domains, I add an new IP, then change the domain to use the new IP, but after that both IP's and the "remove Link" remain "greyed".

This is really frustrating :(
Is there a way to force unbind an IP from a domain?

Thanks for all your help.

Rodrigo