I was thinking its a bug if you lose membership to the Mage guild and havnt accepted to join another guild. I should only lose membership to the Magic Guild if I accept to do join the Mercenary Guild. But, at the moment when i 'T'alk to Cashin I lose it straight away. ie I dont even get to read the first sentence of introduction. You become a mercenary male just by clicking 't' (This is while his info message is still on the screen and not having accepted to do the quest). I am thinking that all the Guildmasters should also warn you that by accepting to join another guild you will lose membership to any other guild upon 'acceptance to join' or succesful completion of the quests to join.
It's currently making me a mercenary male and I havnt accepted his quest or completed any quests. I'm redoing Mage quest and will hit
't' on Cashin to make sure this was the case.
Edit: OK completed the mage quild quests again went back to the quild master and after accepting to join am now a male human wizard again. I went back to cashin and he now asks if i want to re-join of which i declined and i am still a male human wizard. this is fine

. I guess i will have to test it with a new char without doing cashins quests or even talking to him and do the magician quest first again.
edit2: Tested with new lev 1 char, became a mage member, then spoken to cashin that i would accept his quest. I'm still a mage memeber..so working fine now.