Malwarebytes reports calibre portable as Ransomware

Thanks to the excellent advice from John T. Haller I was able to transfer my large calibre portable library into the portableapps version of calibre portable. Unfortunately, Malwarebytes is convinced that calibrePortable.exe is ransomware (Malware.Ransom.Agent.Generic) and keeps quarantining it. Can anyone explain this behaviour before I make an exception in Malwarebytes?
Regards