Under Windows, pressing CTRL-C when nothing is selected clears the clipboard.
This is a problem when you copy something and then for pasting you mistakenly press CTRL-C instead of CTRL-V. In Mathematica 9 and other standard windows programs, pressing CTRL-C with nothing selected does not erase the clipboard but now in v10, if you make this mistake you need to go back to the source and copy again. This reduces my productivity,
This sound like a very small issue, but I have done the mistake enough times that I would like to draw attention to this and know if other users also feel affected by this problem.
When I want to copy two or more items from different places, I paste them first on TextEdit or Notes. Then I can use them as needed, sometimes more than once.