I find that when I try to copy and paste using the CTRL+C and CTRL+V shortcuts, often I have to press CTRL+V twice before the symbol appears on the cursor to paste. In some cases, the previously pasted object appears instead of the currently selected object.
Depending on the copy/paste sequence related to other schematic operations (including mouse, object selection), keyboard actions may not get the proper focus on the objects.
This problem has been fixed in the latest 10.1 Service Pack available at:
The first service pack containing the fix is 10.1 Service Pack 2.