JOSM - Save file dialog triggering weird re-scale of buttons?

Occasionally, when I do Ctrl+S to save a .osm file, something strange happens to JOSM after the dialog appears. A few things shift around slightly, and most notably the pin and close buttons to the sidebar sections get much larger, as shown in the screenshot below, circled in red:

(Sorry for the huge image; I don’t know how to make them smaller here.)

I haven’t yet figured out a pattern as to what causes it; it just seems to happen randomly if I open the save dialog. It’s purely visual, and doesn’t affect any functionality. I haven’t found any setting or anything that will change it back; only a restart of JOSM fixes it. It’s not at all a significant bug, just a weird minor annoyance worth noting. Any idea what causes it?

Please report this via a josm ticket by clicking in josm on menu help → report bug after this happend next time.