Go to http://www.reddit.com/r/videos/
Click on a few of the "video expansion" buttons (to be able to view the videos via an embedded player, right there on the same page.)
One or two will display, but after that, the rest just show as empty space.
See screenshot:
What's most odd about this bug, I have found, is that even if I disable Adblock Plus (using the toolbar button) the problem does not go away. Nor does go away if I add "reddit.com" to the list of whitelisted domains.
HOWEVER, the problem DOES go away if I disable (or uninstall completely) the Adblock Plus extension via Safari's Preferences pane. Seems weird to me that disabling that way renders different effects on a webpage than disabling via the toolbar. Still, I view embedded videos quite a bit (especially on Reddit) and can't keep Adblock Plus enabled/installed if it's going to interfere in this way.
This is 100% reproducible for me.
Thanks for the attention.