Currently, when you delete a secret key from Kleopatra you get asked for confirmation twice by Kleopatra and then gpg asks via pinentry window for confirmation for every subkey.

So you have to confirm 4 (!) times for the deletion of the key.
And if you do not always answer "delete" you may end up with a key with out primary. Which is probably not what the user intended.

Please remove the pinentry dialogs and delete the whole key after the second confirmation.