Contents of other folders visible briefly

Hi, I have a small problem and I'd like to know if it can be fixed.

Upon opening a folder, sometimes the contents of a previously opened folder become visible. They flash up for about a second or two before Vista 'refreshes' and reveals the actual contents of the folder opened. I opened a folder recently and saw my brother's files that he has kept secret for a birthday surprise.

The contents in question are in a folder recently opened by my brother (but not even the same day, as I asked him and he said he worked on it last a couple of days ago - before the last restart).

It happens quite often and I want to know if I can stop it happening again so I don't ruin more of his surprise.

Surprise spoiling aside, I've always found it irritating, and it never happened on XP.

Thanks for reading - the problem is kinda hard to explain in only a few words.

 

Has nobody else noticed this in Vista?