Lately I have a problem with this. Clicking "I've checked all of these" will fail randomly, in maybe 1 out of 10-15 times. It seems to work, as the Newest Nodes page I get back after the click is indeed empty (modulo new posts) as it should be. However, refreshing Newest Nodes reveals the flag wasn't updated as all the old nodes that shouldn't be there reappear.
Very irritating if it's the last thing I did and then come back a day later to find all of the old nodes still on the list with no clue at which point to check in. :-/
As "I've checked all of these" works (when it does) across several different browsers/computers that don't share cookies, I have to assume the problem is server side. Or is it? Maybe it is really a browser issue? Has someone else had the same problem and fixed it?
FWIW, I'm using Mozilla 1.0 RC2, build 2002051620, on a Linux 2.2.20 box.
Makeshifts last the longest.