RobotStudio -- one line "stuck" highlighted

RS 2023.3.1.

This is a silly, purely cosmetic thing, but it keeps jumping out at me whenever I scroll past it:

That little box around the values of the PERS EndCapPart. It's always there, no matter how many edits I make, or how may times I reboot the robot. That variable is declared but not used anywhere (I might just eliminate it). But I have no idea if that box means anything, or it's just a graphics artificat.

Well, it's odd. If I change the name of the variable, that line stays highlighted. If I change the line to a comment, the highlighting goes away.

But then it got weird: I created a new (unused) variable of the same type, different name, same value, directly below the commented-out original, and immediately got the same highlighting on the new line.

Then I created another new unused variable several lines above the original. That line did not get highlighted, but the first new-unused variable stayed highlighted.

Very puzzling. Seems to be harmless, it just bugs me...