1.: that should not happen. We would need the Performer project (the .xml file) and your Cuabse project (no audio files, just the cpr) to check (send me a PM).
“Please consider adding a new feature which removes partial files from an aborted transfer.” Problem is that we don’t know. When you suddenly end Cubase while a transfer is still in progress, the transfer is aborted. Would be quite complicated to try to resolve this.