Update a local copy don't works at second time

[hpsaturn]

Overview

When I want write to my local disk on an opened Gist it only works the first time. The second time I only have a Gist update and I can't save changes in my local. How I do it?

Reproduce:

:Gist -l
choose an old gist
make some changes
:w! ~/xxx/my_local_gist_copy   <== it works fine, write in my local
:w! ~/xxx/my_local_gist_copy   <== it only update the Gist
:w!                            <== it only update the Gist