Correct me if I'm wrong, but I think the "Mark forums read" link does not actually mark the topics in the current forum read, just the subforums in it
I just tried it out and you're right (only tested it in a category-only forum before). So the confirmation message should instead say "All subforums of $forumtitle have been marked read" or something similiar.
or by giving users a confirmation box when they clicks the mark read link that would allow them to specify among several options.
I guess that would be too much for a bugfix. IMHO the feature itself can stay as it is - just the message should be corrected because it currently says all
forums have been marked read, which is not the case.