Signing and encryption controls not being rendered

I'm writing a security extension which implements the MEMessageSecurityHandler protocol. The problem I experience is related to the encodingStatus method as defined here.

The problem is that when I return the following MEOutgoingMessageEncodingStatus instance the signing and encryption controls don't appear even though I believe they should:

MEOutgoingMessageEncodingStatus(
            canSign: false,
            canEncrypt: true,
            securityError: nil,
            addressesFailingEncryption: []
        )

Any other combination of the canSign and canEncrypt properties does generate the expected output.

So... is there anything I'm missing?

Thanks a ton for your time!