iBooks constantly runs out of memory

I'm creating an iBook with HTML widgets that contain some .mp4 videos.

The iBook has several of these widgets. If a user is reading the book, iBooks usually crashes with a low memory error before they can even get to the 3rd one. This is extremely annoying.

Why does this happen? It seems to me that, when someone loads a widget and then closes it, the widget still remains in memory (since, if you reopen the widget, it's in the state that you left it in). This seems like a pretty huge memory leak.

Is there any way to force iBooks to free that memory when a user closes the widget? I'm OK with clearing the state of the widget when they close it. These low memory issues are starting to get ridiculous.