sometimes fails to block? Rated 5 out of 5 stars

Great addon, always been solid, but just recently it's been intermittently failing to stop *some* flashvids. I haven't yet seen what triggers this.
I follow a link to youtube, say, & it's blocked correctly; I go on to a related tubevid & ~sometimes~ it fires off straight away, even if I reload the page. Very odd.
Nothing whitelisted.
Happens on FF 12 for mint 1.0.

This review is for a previous version of the add-on (1.5.15.1.1-signed).