I see this on Safari 12.1.1 on macOS Mojave 10.14.5. I have not tried other browsers.
- Bring up the Identify panel
- Click Add ID so an ID field + comment field appears
- Type a character or three in the ID field so a list of suggestions appears
- Hit the Esc key on the keyboard
The Identify panel disappears, but the list of suggestions does not. It hangs around even if you bring the Identify panel back up again, and is in the way in that case. Reloading the page will fix it.
This does not happen if you close the Identify panel in step 4 by clicking the X in the upper-right corner.