[bad_captain]

I suspect the issue with this code from ClientPacket.cpp, handling the group invite:

if((!Invitee->IsGrouped() && !Invitee->IsRaidGrouped()) ||
				(Invitee->GetGroup() && Invitee->CastToClient()->GetMerc() && Invitee->GetGroup()->GroupCount() == 2))
			{
				if(app->GetOpcode() == OP_GroupInvite2)
				{
					//Make a new packet using all the same information but make sure it's a fixed GroupInvite opcode so we
					//Don't have to deal with GroupFollow2 crap.
					EQApplicationPacket* outapp = new EQApplicationPacket(OP_GroupInvite, sizeof(GroupInvite_Struct));
					memcpy(outapp->pBuffer, app->pBuffer, outapp->size);
					Invitee->CastToClient()->QueuePacket(outapp);
					safe_delete(outapp);
					return;
				}
				else
				{
					//The correct opcode, no reason to bother wasting time reconstructing the packet
					Invitee->CastToClient()->QueuePacket(app);
				}
			}

I'm not sure it correctly handles removing the invitee from their group before trying to add them to the other group, if at all.

I'll try and test it thoroughly this weekend.