I have never seen this before and have been so far unsucessful at finding anything out about it.

I redid my UI and cleaned out my addon and WTF folders and installed new addons. Opened up wow and when I go to invite my team with ISBoxer shortcut They join the group then leave, the same thing happens if I use the Jamba command. If I disable Jamba addon and do the same team invite all the toons join the group.

I have setup the team in Jamba and have it set to auto accept group invites from team, guildies or friends. Last time I set up Jamba I don't remember ever having this issue.