Pictures 'vanishing' in Trash

Hi,
I have a MacBook Pro with Lion and there's a bit of a problem with the trash can. When I deleted pictures from a pen drive, i.e. dragged them off into the dock trash can, they disappeared. Sort of. I opened trash, saw a few of the pics for a second but then all were gone when I checked again after a few minutes. This happened only with pictures from a pen drive, all the other pics (downloads, etc) are in the trash. I want to make sure I won't delete something I meant to keep so it would really help if I could review the contents before emptying the trash can.
Any ideas what I'm doing wrong? Maybe somebody had the same problem? I'm a new Mac user so there might be a simple fix I don't know about.
Thanks for your help,
Julie

Yes, the pictures are in the Trash as long as the pen drive is plugged in, and are only deletable while the pen drive is plugged in. Once unplugged, they disappear from sight and cannot be deleted until the drive is plugged in again.

I've moved your post to a more proper forum; please be sure to check the forum descriptions to find the best place to post.

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Thanks for understanding!

Thank you! Just joined this forum today and wasn't sure where to post my question

@McYukon: Bingo! Plugged in my pen drive and the pics showed up in the trash. Thank you!

Your welcome