[paperback]

Linux Mint 20.1 / Calibre 5.38

1. Open the "Insert special character" window and select "Greek extended" (for example).
2. Enter a few characters, then select the "Greek and coptic" heading.
3. Press the space bar.

Expected result: A space should be entered in the text.
Actual result: The dialogue closes (because focus has switched from the text to the "Insert special character" window).

The workaround is to insert the space before you change headings.