Comment 2 for bug 1029371

This doesn't only happen if done too quickly, this fails randomly about 50% of the times. Even if you wait for the left launcher animation to be completely done before you drop (which I now _always_ do), the drop still silently fails at random times.
Usually, when you redo it a second time it works. But there are times when I retry again and again and it keeps failing, until I deselect, reselect the files and try again and it works.

This is tremendously annoying and it's been already more than 6 months.
It's also DANGEROUS: if you don't realise the copy has not been done, you may delete the original files thinking you have already copied them. Importance should be raised.