I’ve noticed if I close a glyphs file with a Category selected on the left (say, Cyrillic > Basic), when I re-open the file, that category is still selected on the left pane, but the main pain appears to be showing all glyphs in the file.
It’s not especially important to me to retain the category selection, but I do think it’s a minor bug worth fixing that the menu and the pane contents aren’t aligned.