Thanks for the report. Indeed I can also reproduce it with my own key. For signatures from expired / revoked / disabled keys it shows "No public key" because GnuPG returns the same error in that case. We can fix that by looking up the key ourself.

Fixed with: https://commits.kde.org/libkleo/245eff174331c49264d1248c529e0276e02e9e29

For my key it looks like:

key expired and key revoked are both new states.