When video crossposting was first introduced, those videos would ignore filter settings in the Subscriptions tab and always appear in the list. But after the recent update(s), it became the opposite: crossposted videos will never appear in the Subscriptions tab, even if all the posters are subscribed and not filtered out by the current settings.
Thank you for reporting! We can filter collaboration videos based on the group filters, however, as I see the feature is not working properly in Firefox, I've prepared a fix in the upcoming version of Firefox 18.5.9 and will be available after review next week. UPD: the new version 18.5.9 is available, and the issue has been resolved.
