Git gui - Commit message lost when changing from New Commit to Amend Last Commit

Hi,

When changing from New Commit to Amend Last Commit, the commit message
it discarded.
It could be appended to the previous commit message with a place
holder or something similar.

git-gui version 0.20.0.1
git version 2.8.0.rc3

Cheers,
--
Marcus Nascimento