Can't sign partially protected Document

There seems to be a problem with the mobile Versions of Adobe Reader. We are creating protected documents where signing is explicitly allowed. But signing of these documents fails in Acrobat Reader Mobile on iPhone and Android with the error message, that the document can't be signed, because the document is protected.

Signing in Adobe Fill and Sign is working however. Signing in Adobe Reader on Windows is working, too.

I would be grateful for any suggestions or aknowledgement, that there is a bug in the mobile versions.