plus one think about Hexblade set weapons.. :So the 5d12 works but it does not stack with the +enh15. If that is the case there is nothing we can do about it. It is a known engine related bug. You dont get +15 slashing damage.
And I dont know why Hex curse counts just half hex level. I like pure class and if you have high level one class, you should have strong class feat. The curse counts as full class level.