unintentional moved file..How many am i deleting?

[sunriser]

I love duplicate cleaner -- but have not studied manual as it seems so self explanatory. i am in the process of moving dups out of my lap and desk tops into one of four drives on my MYBOOK terra station. recently i've been selecting "everything" --then selecting �all but one� duplicate of groups and moving these �all but one� duplicates to the terrastation to free up space. (1st issue) i don't understand why running it a second time, say within a day -- picks up new files?? but (2nd issue ) most importantly-- this morning i went to get a photo for a rental ad i have been posting regularly. and although photos A, B, and C were in the folder (desktop of desktop) as usual -- photo D was not! and it was nowhere on my desktop! fortunately i found a copy...in my lap top back up drive of My Book!!! (the photo D is on my laptop as well). so...it photo D was somehow erased from my desktop. very scary! how might this have happened? maybe an amateur such as me should not be messing with this? help, someone!