Some recent documents show up in Vista and others don't.

I have Microsoft Windows Vista Home Premium for my laptop. When I open some Microsoft documents some show up on the recent documents list, but others don't. I don't understand why this is so. It seems so random.

For example, I opened up two word documents. Let's for example, say A and B. Only A showed up, whereas B did not. It happens for some Access files, and some Excel files too.

Also, is there a way to set the recently opened documents list so that files with a certain extension don't show up on it? I only want work related documents to show up on the list, so no video files.

Any help would be greatly appreciated.