Hmm, well, Facebook changed way of notifying about contact status changes, but still support the old way (old request for polling buddy list). But maybe for some users/computers it was somehow changed...
I don't have this problem so I can't fix it by myself. But it's weird that it works on different computer for you...
I would need to have some HTTP logs from that broken account to fix it. You can install
Fiddler, capture communication for Miranda's FB plugin - you need to start Fiddler and set HTTPS proxy in Miranda's options / networks for the Facebook account. To address 127.0.0.1 and port 8888. Then you will see in Fiddler all communication going via Miranda. And that's what I need - you can save that log, capturing communication containing /buddy_list.php requests (I'm interested only in these), save them and send them to my e-mail. But don't share these logs elsewhere publicly as it contains private data.