I screwed up big time on the update 8 fix for the left steady arm pose, I reposted it. So if you used the fix, you will need to redo it with a version of the model BEFORE the original fix. If you don't have a version before the fix, you can send me the model and I'll fix it for you.
The problem is that the pose fix wasn't set to it's default position in the user properties (0%). So if the pose was set to (-1), the arm may have moved from it's default position in the action and exported like that. This will cause your model to not be symetrical (geometry and bones) and will cause issues with mirroring pose.
This is a major problem and I'm sorry for any inconvience.
For the fix, import the update 8 fix model, turn OFF IK legs, IK arms and all spine poses in the user properties. Create new action and export model following the instructions.