the announcement for xenforo 1.0.2 was posted 44 minutes ago but it was hidden.
almost 30 minutes ago i clicked on "mark all forums read", when the announcement was made public, it appeared as "read" to me. I suppose it shouldn't
There's no way around this. In general, it happens when threads are moved. The forum is marked as read as of time X, but if a previously unread thread with time < X gets moved there, the system thinks it's read.
Ironically, the only way around this would actually make a mark all read function completely infeasible.