I am realy stumped by this. I just noticed that I had a new PM, but no flashing indicator. That's on our board running 7.5.

So that gave me the chance to do some testing.
tried refreshing the page several times -> no luck
cleared the cache -> no luck
logged off and on again -> no luck
closed the browser (FF 3.0.6) and restarted it -> no luck

So I started another instance of FF to check some data in the database directly but couldn't find anything wrong there.

Then, while still in my second FF-window, I open the forums and tadaa there is the flashing indicator.

Now back to the first window, press F5 and tadaa a flashing indicator here too.

I haven't got a clue where to search in order to tackle this problem, but maybe it gives someone else an idea....

Hmm, were you auto-logged in on both instances of firefox, meaning are you remembered on your forums, or do you have to login each time?

Usually I am auto-logged in, but if you manually log out, you have to manually log in again too.

So in the first FF window I was logged in automatically, but no indicator. Then logged out manually and closed FF. Then restarted FF and logged in manually. No indicator.

Then started the second FF window and there I was logged in automatically. In fact the same situation as with my first startup in the first FF window.

I have the same problem, but actually the indicator is there! But only the image is not showing. When you hover over the place the icon should be, you can click it and you go to your new messages. Always found this to be a weird bug, but it's there since 7.1.

I have got no clue why ffox is not displaying the image though.

I do recognize that problem too, but that's not the same as the situation I described above where I don't have an image. If I look at the html code in source view, there is no image, nor an image link.

Back to my original prolem:
I did have the exact same problem again once today. That was on my first forum visit of today. On all other occasions of new PM's, the notifiction showed as it should.

I also got message from another forum member who had the same experience. He was logged on and there was no indicator flashing.
As soon as I sent him a PM, he noticed the flashing envelope and went into his PM mailbox, only to discover that there was onother unread message waiting for him since yesterday.

There is one similarity in all occasions that I have recognized thus far, and that is that those non-indicated PM's were sent on day x, while the receiver was logged off. And where the receiver didn't log on until the next day.

I will keep watching for any predictable behaviour.