I have found that meanwhile too. But I do non understand why it should not work with WinSCP. May I have your sshd configuration file and/or logs files showing connection attempt with both allowed and disallowed scp fallback?
Before posting, please read how to report bug or request support effectively.
Bug reports without an attached log file are usually useless.
Can you point me to some documentation regarding the new functions?
I guess I understand what ChrootDirectory is. But what is internal-sftp?