So I just notice that Silver weapons are much more stronger when I become a vampire.

I tested this with only the Vanilla plus Unofficial patches.

When I'm not a vampire the Silver Sword shows 9 points of damage.

On becoming a vampire the damage turns to 29.

Any way to fix this?

I know Silver weapon are more effective against vampires and some other creatures.

But the problem here is that now they are 20 points stronger to any other creature if you are a vampire :/

Haha, looks like you confused the Silver sword!:'D
But if this is actually how they work this is a pretty interesting oversight!