Files lost after Windows cut-and-paste

[#1]

Last week I was assisting someone to cut and pasta a large volume of files from the computer hard drive to a memory stick.  After the operation had finished we discovered that many of the copied sub-directories were empty and their contents had been lost.  The only explanation I can think of for this is that the memory stick was a fake of a type that reports more capacity than it actually has.  When it was full it just junked the remaining files whilst reporting back to Windows that they had been copied.  Any thoughts or alternative explanations?  I tried to simulate another possible cause of the problem with a different memory stick by removing it mid-way through a cut-and-paste but no files were lost.          

[#2]

I think you've hit the nail on the head there @ReedRichards, so this link may be of interest to you.

[#3]

I used win-merge to compare directories. I normally start off a big copy that has not finished before I must turn off the computer, so I have to cancel half way through the copy.

[#4]

It's for the same reason I use copy-paste. That way you keep the originals intact while you check to see if all have gone across.