In my forum subscriptions I see there are new posts. I go read them, but the My Forums list still shows there are new ones. Likewise, none of the subscribed posts are refreshing to 0 after I read them.
If I understand you, the new post indicators and counters on your My Forum page are working as they always have.
Near the top of the General Preferences section on your preferences page you will see a Reset last visit: option. To the right of that you will find a What's this? link. Here is part of what that link will tell you
The forums keeps track of when you visit and when you leave. After you have been inactive on the forums for a certain amount of time your last visit time will be reset. This is what determines whether new post icons are displayed. By default the forums resets your last visit time after 30 minutes of inactivity.
The new posts icons and the counters on your My Forum page does not tell you what you have read or not read, but rather what subscriptions have had post added (and how many) since you have been idle on the forum for whatever time you have specified. (BTW, there is a trouble ticket in about the "specified time" not working. It seems that it is always 30 minutes, regardless of the preference setting.)
At the top of each sub-forum's topics list, there is a Mark As Read link that will change the new post icons to no new post icons and if those forums or threads are in your subscriptions, the icons there will change and counters will be set to 0.
counters reset properly on one computer, not another. hmm...
I have no explanation. Although I've never really checked, I believe the times are kept in your account on the forum's servers. I did just check on another computer that I haven't used on the forum all summer. When I logged in, the New post icons and counters were the same as on the one I was using when I first read this message.
BTW, on the My Forums page, if you are subscribing to a forum, the new post icon indicates a new thread has been started. There could be lots of posts added to existing threads and, as long as a new thread hasn't been started since the last visit, the no new post icon will be displayed and the counter will be 0.
Topic and member subscriptions and indicates new posts in the thread or by the member.