Video Window will not maximize

Hi there,

I've recently run into this issue in Safari and I can't seem to figure out why it happens. I have been watching video courses at creativelive.com, and if I watch one video I am able to maximize it to full screen. Once that video ends and I restore it to normal size and start the next video, I am not able to maximize the subsequent video. It seems to try as sometimes I get a "flash" of a full screen image but it then makes the tonal "plink" sound as if I am doing something that I am not allowed to do. Closing Safari and restarting this video allows me to maximize the video window to full screen once more, but the process repeats itself if I try to watch the next one.

Any ideas as to why this happens, and what I can do to fix it?