It was brought to my attention that the wording for Unbalanced could be interpreted as wielding such a weapon gives a -10 to ALL parries, not just with the unbalanced weapon, meaning a sword in the off-hand used to parry would take a -10, cancelling out balanced. Is this how it is supposed to be interpreted?

I really don't think this is the intention. After all, this would make dual-wielding with Unwieldy weapons (which can't parry at all) much better than dual-wielding with Unbalanced weapons. So... you can easily parry with a Power Sword/Power Fist combo, but not with a Power Sword/Power Axe one? That's... probably really, really not intended.

The correct wording should be "impose a -10 penalty to any Parry Skill Tests when parrying with this weapon".