"Explorer 3.01 (as well as previous Explorer's I've run) saves the location of its cache folder by Volume-Reference. This is not recommended by Apple. This can cause the problem with saving cache files to ShrinkWrap etc.
A Volume-Reference is basically an index to the mounted volume. If you sometimes mount external drives, network volumes or any other volume (CD), it will cause the index of your temporary partition (which is mounted last) to change. Explorer will not notify you of this, it will simply start using the Explorer Cache folder in your Preferences folder. The only work-around I can think of is to check your cache location in the Advanced Preferences setting when you start up Explorer."