No visual indication is provided when an unavailable spell fails to be chosen via a quick key
Press F1 and create a shortcut to a spell
Delete the spell from your spellbook
Press F1 again and the spell will still be there
(RM-4391 from redmine: created on 2018-04-12 by jgut ., , closed on 2018-04-19 by Alexei Dobrohotov)