Any clue as to Why my U3 drive is faster?

When I shut down my U3 drive, the USB drive is ready to remove in a very short time, just a few seconds. When I use the same drive with Portable Apps, the drive will often read/write for up to a minute and a half before it is ready to remove. The difference seems to be Firefox as the U3 uses 1.5 and Portable Apps uses 2.0.

Is there something else I should be doing? The drive seems to be deleting cache files, while for some reason, the U3 version does not seem to do this.

Much thanks.