When the timeline cursor hits on a key frame the Add/Remove button changes to '-'. But the one on the right hand side doesn't change.

Since I work with full screen of project monitor I have to watch the cross in the middle if it's larger that means I'm on a key frame.
Unfortunately, I still make the mistake that I believe I'm adding, but I'm actually deleting.
I wish the button can change like the one in the effect panel.