How to force OS X Preview 5.5.1 (719.16) to "refresh"?

I was using my iPad2 to capture some screen dumps from my App. But I found that when I tried to use Preview (Version 5.5.1 (719.16)  running on OS X 10.7.3) to "Import from iPad2", the displayed content never change even if I made quite a few changes on the device (new images been created or old ones been deleted). Which means the latest updated images can't be imported to my MacBook.

There must be a time-out or cache refresh interval period defined somewhere, but how long do I have to wait or how can I force it to refresh?

I tried disconnect the USB cable and reconnect again, still the same. Tried deleting some images from within Preview, still the same.

Very strange, and I can't find any function in Preview to force it to refresh/reload. Quite annoying, I guess the last option is to restart my MacBook Pro (Update: yes, restart did force it to refresh). But that's quite dumb if you have to reboot your Mac just to refresh Preview??

Any one got similar problem or have any idea how to fix this?

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