Your comments

yes please, it also makes it very tricky to move the border.

this workaround does work. 

however i would concur that it his highly confusing that the global settings are overriden like this.

also, i am hard-pressed to find a reason why this should not be a default, or what's different about osx that it would be disabled there.
yes, the current behavior is counter-intuitive and unlike other editors. 
yes, the white highlight is next to useless for those of us using light themes. 
you're right, hadn't noticed that.