Before 4.0.1, when an Arcane Mage polymorphed a warrior into a Spell Reflect, the polymorph would go onto the mage, and act as a normal polymorph would; healing over the 10 seconds, and breaking when the target is attacked.
Since 4.0.1 came out though, it seems that if you have Imp Polymorph, the Spell Reflected polymorph never breaks until the full 10 seconds are up.
What this means for Mages: Free healing with no interruptions.
What this means for Warriors/any other class with a spell reflect: A timeframe to out-damage the heals, and basically pound on the mage for 10 seconds like you would if they were stunned.
Could also serve useful if you were planning on using the spell reflected poly to eat/bandage, but still had a bleed/dot up on them.
It's pretty nice exploit for mages in a situation where you need heals and your opponent has a spell reflect ability, and also nice for warriors that feel like having a 10s stun.
Here's a video for proof of the exploit:
YouTube - Arcane Mage Poly Exploit
Hope this helps!
-SL