I have several users experiencing this problem, however I am unable to reproduce this myself. Our host is oldgmctrucks.infopop.cc .
The initial reporter is a frequent experienced PM user, so he understands how the system works. Since last week (likely Friday, he believes), he finds that if he gets the "New PM!" flag and reads the message, the flag does not disappear. This continues across different signons. He also has used Ctrl-F5 with no effect. His platform is Windows 7 using a Firefox Browser.
My experience is as it should be. I also run Windows 7 on my usual machine, using either IE or Firefox. It worked on IE and Firefox 43.0.4, and I upgraded to 44.0 today and it works properly there, too. I believe 44.0 was made generally available yesterday, Jan 26.
I would think that this problem would be consistent for all users, as I believe that the record of the read of a PM is kept on your host. Some information is kept in cookies, but this feature remembers on different computers or platforms, so it must be host based. That would imply that the client machine is immaterial, however not all users experience this problem. Odd?
Can you offer any insight or suggestions?