Hi,

After the following steps:

- Start a capture.
- Move to end of capture buffer (M->).
- Type some text.
- Abort capture (C-c C-k).

the capture is aborted but its contents are not removed from the
target buffer and the following message is shown:

  "Capture process aborted, but target buffer could not be cleaned up
  correctly"

I am a attaching a patch that adds a test case showing up the problem
and includes a proposed fix (setting the capture kill end marker
insertion type).

I am not sure whether the fix might affect something else.  Does the
fix makes sense?