Hi Daniel @Dakkie15 ,
It is because of the Bevel Modifier; you have the Material for the newly created Faces set to Automatic (Index -1). That usually works fine, but in this case it doesn’t. If you set it to the second Material Slot (Index 1), every Beveled Edge will get that Material:

That is a nice effect, but might not be what you want.
So, your solution of separating the handle is probably the best.