Hi queenofcollectibles,
Thanks for pointing that out. I admittedly found myself scratching my head about this earlier today since all the buttons in the description editor toolbar are colorless, but I was able to see similar behavior after clicking the “Insert Horizontal Line” button and then mousing over the line that was created.
I confirmed that the red arrow button works just as you described, and hopefully that information will help the original poster work around any difficulties this option may be causing.
-Mike