The only times Youtube does that on mine, is when the available memory(not storage) gets overloaded and the phone is forced to cut the browser off. If you can pay attention to how much of your ram is being used at any one time, you'll be able to avoid this more easily. Apps like advanced task killer task killer and zdbox are quite useful in measuring and managing your ram usage.
It really helps not to use too many apps and/or processes at once, because they will slow each other down or make the other larger memory using programs(like the browsers and youtube) become inoperable.
The phone can only handle so much at a time, so even if everything else is working as it should, your available ram can be a hinderance if unchecked.
I use 2.3.2(gingerbread once again) if it makes a difference, so our phones operate similarly.
edit: Then it sounds like a problem with the file type that was being used for some of the videos or a signal issue.