To reprouduce:

• Use empty keyring.
• Import Pubkey X (but don't certifiy)
• Verify signature made by X.
• Open Details in verifcation window.
• In that window select the UID and certify.

-> You will asked to generate a new key to do the certification.

• Click yes.

--> Newcertificatewizard won't accept input.

There is probably a modality / parenting problem.