Just a guess here: Could it be related to which window has the focus?
That brings up the question, do you use an IDE with individual windows, or do you use anchor-docking (and if so, a single Window or several groups)?
Or maybe it depends on some hint being shown when the issue happens? Or any other menu, popup-menu or drop-down is open when it happens? (Some Linux desktop managers have their own peculiar rules on how they handle such things.)
Can you visible (grey out) see, if the down-arrow is enabled or disabled?
If you do not use anchor docking:
- Does focusing the main-ide-bar make a diff. Well that is, how the focus is moved to the main-ide-bar.
Obviously, attempting to click the down-arrow does focus the main-ide-bar.
But if you first move focus to the main-ide-bar, before/without clicking the down-arrow (also not clicking the button that has the down-arrow). E.g. Click some icon in the component palette to move the focus.
- If you tried the down button and it did not work => move the focus away (e.g. to the source editor), then to the component palette, and then test the button again.