I've never had any use for REAPER's drawing pin (thumbtack if you're a Merkin) thingummies, I don't really know what they're for, and I prefer to ignore them.
I've noticed that Melodyne causes a strange graphics glitch when I move the FX window, leaving the ghost of a pin behind it.
These ghosts hang around for a while, but go away eventually once they're off the screen. The really strange thing is, I can push and pull them as if they were really a thing....
It's curious, and I thought I should report this for the devs' information. It doesn't bother me.