Please describe the problem:
If you close a message window which was the source of a copy operation, then you can no longer paste.

If you minimise the window instead, then you can paste.

This happens whether you are pasting outside Evolution or into another message.

This happens with email addresses as well as body text.

Steps to reproduce:
1. Open a new message
2. Type something
3. Select some or all of the text
4. Copy (Ctrl+C or from the menus)
5. Close the window, selecting "discard"
6. Open another new message
7. Paste (Ctrl+V or from a menu)


Actual results:
Nothing.  The clipboard is empty.


Expected results:
The copied text should appear.

Does this happen every time?
Yes.

Other information:
If you don't close the first window paste works.

This suggests to me that the clipboard has been implemented as a reference rather than as a copy.