org-capture-kill (C-c C-k) used to abort capturing puts the contents
of the capture buffer into the kill ring.
This is obstructive when the user wants to abort a capture, but save a
portion of the text into the kill ring to yank elsewhere. The aborted
capture contents will replace the desired content.
I believe that's a good fail-safe mechanism. Imagine the joy when you realize that Org simply saved your incomplete capture in the event you kill it by mistake!
FWIW, I have never needed to make use of that failsafe mechanism, nor have I ever needed to copy something from my capture and then kill it. The use case you mention seems to be very rare IMO.
Aborting capture should act transparently like killing a buffer. It
shouldn't affect the kill ring. If the user wants to keep the capture
contents, he can trivially run C-x h mark-whole-buffer M-w
kill-ring-save
You can always C-y M-y to yank your second-last kill, C-y M-y M-y for the third-last kill, and so on ..
To summarize:
- Current behavior helps users lose their incomplete captures by mistake.
- In the event you want to copy something and deliberately kill the capture buffer, you can always paste it with C-y M-y.