I was messing around with my Barb and i found something weird.
The passive bonus applied due to WEAPONS MASTER (WM) wouldn't change no matter what my Main Hand was.
Check this yourself:
1. Unequip all your gear
2. Change All your passives (make sure you do not select WM)
3. Equip your Main Hand
4. Equip Off hand
5. Select WM passive and the other two desired.
6. Equip rest of your gear
7. Now you can change your Main to whatever 1 hand weapon type you desire and you keep the passive bonus you had when you did step 3#
Feel free to comment, criticize, ask for help, and if you liked this in any way give me some feedback
Don't know if this can be used for any other kind of exploits.
Regards