Exception in AWT-EventQueue-0 with SelectDropDownList

Hi!
I’m using Polyscope 3.5.1. In my URCap, I’m updating the options of a SelectDropDownList based on some message received via TCP/IP. In some cases, I see the following error message:

I’ve never seen it in 3.4.x.

One more clue: I’m using setItems method with a list of strings to update the list. Whenever an update is triggered, I update all the program nodes that are available (not just the one that has the command window opened).
If I close the popup, everything seems to continue normally. It doesn’t seem like a serious bug, but it may be good to know the cause.

Any ideas?

Edit: I’m asking this here because all those lines in the stack trace aren’t coming from the URCap’s code.