Thanks for your further thoughts mAsT3RpEE.
Your understanding of the technical issues involved here is obviously far advanced compared to mine.
But I do now understand what the 'og' title is that WP SEO generates, and the potential for it to cause exactly this type of problem.
Looking on the forums; many other people have had many similar experiences to me: messed up titles using WP SEO.
I'm not sure Yoast's plugin is the best - SEO Ultimate has some excellent features that Yoast's doesn't have, without the risk of ruining your ranking with this Open-Graph S*#t!
"Currently the plugin has no support for videos from what I've seen in the code."
I hope you're referring to the (free) WP SEO plugin - and not the (paid for) Video SEO extension.
I paid $69 for Yoast's 'Video SEO' extension in order to optimize SEO of videos, but that's when all this trouble all started.
I have been loathe to get rid of WP SEO, simply because another gentleman has written a very useful plugin which integrates the Shopp ecommerce plugin with WP SEO (SEO glue).
I am going to try deleting just the 'Video SEO' extension first (even though it cost me $69).
If that doesn't fix things - I will most definitely be going over to 'the dark side' (swapping to SEO Ultimate).