From the mailing list:
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On Tue, 8 Feb 2005 11:35 am, John P. Rouillard wrote:
> While I can understand collisions on regular fields, just
> submitting a file attachment or a change note
> shouldn't be able to cause a collision since they create
> entirely new messages/links which can't collide.

Yes, since they're both just an append operation, it
should be safe to go ahead with the edit. I'd be
comfortable with this being changed - it'd make
the code a little trickier though.

> Even if you disagree that the change note/file upload's
> can't conflict, the values of the change note and file
> uploads should be preserved in the reload since there
> is no change that could be made to this issue that
> would override these fields.

You actually can't preserve a file upload over a submit, 
but you can do so with a textarea, and we should. I'd
classify the loss of the change note as a bug.

    Richard
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So here is the bug report 8-).

-- rouilj