Spam on OX - X-Spam-Flag

Recieving mails via ox leads to a wrong seperation of spam and non-spam.

Mails with
X-Spam-Flag: NO
go into the spam folder and mails with
X-Spam-Flag: YES
go into the inbox, even though the manual spam-learning-system has been feeded accordingly.

Also internal mail traffic is been classified as spam for some accounts on the same domain.

Mail client is the ox interface and AppSuite-eM-Client(Windows).