Setting left locator causes weird behavior

Hi Everyone
Sorry, I wish I had a more explanatory headline but I’m trying to set my left locator by holding the Option key (I’m on a Mac) and left mouse click on the bar track.
It work if there’s little to no movement of the mouse. However if I move the mouse over the bars track a reddish overlaying band appears in the top and bottom area of the screen which block the mouse click and messing up what I trying to do.
Also a grey hand appears in the center of both reddish bands. I can drag the bands out of their position, but the jump back once I let go.
It only happens when I’m holding Option and moving the mouse cursor within the screen area of the reddish bands and it goes away if I let go of Option and move the cursor elsewhere.

Any help to both understand why it happens and how to fix it would be appreciated.

Cheers - Anders

Fixed it! I recently installed Smart Scroll to let me do vertical and horizontal scrolling with mouse movements. Really nice when using a track ball mouse. Anyway, Smart Scroll has a feature called “Hover Scroll” which caused the issue.