I wonder if you have a mouse hooked up when you see this. I have looked in vain for a similar bar (I know it's small), but I can use it (can't see it so much) when I hook up a mouse (I am using a touchpad on a laptop).
However, when testing this unmercifully on this go-round, I discovered that, if I did it often enough, the list started scrolling with the two-finger gesture on my touchpad. Once it works, it works for the duration of the user session (the time I'm logged into the computer, not into LiveCode). This strikes me as a memory issue.
Here's the really irritating thing about this. Last time I tried this, I got a "Set Location to Default" box (1/4 inch high by an inch wide) that followed me around from one application to another (though I couldn't discern its origin at the time). Now, I've got the whole SVG list dropdown pasted on my screen, going from LC to Edge to File Explorer (yes, I'm using Edge because the latest version of Firefox gives me a big black screen). The dropdown is live, too, not just a video artifact. You can still scroll it. Fortunately, unlike the previous box, when you click on this one, it goes away.
Thanks for pursuing this issue.