[otrs] "New message!" alert is gone...

Hi We recently updated our OTRS from 2.3.5 to 2.4.7. Since this upgrade the alert "You have 1 new message(s)" is no longer shown, even if there is 1 message in the "New messages" folder. Further more, the red "New message!" text doesn't shop up either. Our problem seems to be similar to the following mail: http://www.mail-archive.com/otrs@otrs.org/msg26394.html What has to be done in order to get those alerts back? Thanks for your help. Kind Regards Raphael Thoma