Thanks, things are clear now.

As it doesn't happen very often then maybe thats what is happening.

Highlighting source directories with control left mouse click then using control c to capture the files.
Then click on flash drive directory then control v.
Its odd it works mostly ok but now and...

When I copy folders to my flash drive I sometimes get "foldername - copy" added instead of the folder being over written.
Does any one know why ?