I have 1 NX5K & 1 NX2K (FEX) and configured PIM on them -Release 5.2(1)N1(1).
I configured on the NX2K's ports the ip igmp join-group command to statically bind a multicast group to an interface. The multicast PIM works fine but when I try to remove the ip igmp join-group command on any interface because not all should have this command, I cannot.
I have not found any bug on the 5.2(1)N1(1) version related to this behavior and the released notes not mentioned anything about this.
FEX ports are meant to be L2 ports only and hence you should not be allowed to configure "ip igmp join-group" but looks like we do allow it which is a bug.. I will see if there is one filed for it and if not file a new one.