question about unread posts and subscribed threads

so... i've got a bunch of threads that i've subscribed to, and what i thought i'd be able to do is go to my sub list and click on the "go to first unread post" button for each of them every time i come onto the forum. but for some reason only one or two of the threads show up with the button, despite the most recent post being hours after i left.

i'm not logging out, but i'm closing the tab that the forum is on. i've noticed the unread post button not turning up for new posts when i'm trawling through the sub-forums as well...

any idea what's going on? does it only work reliably if i log out each time i leave?

soo.... nothing?

aaaaaand again....

I believe it may be both server capability limits and you read all of the posts in that thread.

Also, this kind of post goes in off topic.