Charmed Monks don't Dual Wield
 

Steps to reproduce:

Go to Howling Stones and fight a monk (spectre). It gets 4 attacks per round.
Charm it. It gets 2 attacks per round.

did you give it weapons? just wondering.

give it weapons to duel wield, we give targin maces to make him quad.

*fights urge to make sarcastic comment*

The bug is that they should DW automatically. At one point charmed mobs were considered pets and would DW just like a skeleton or elemental over L35 or so without weapons. This was fixed and my guess is the fix broke monk pets dual wielding automatically.