http://meta.wikimedia.org/wiki/Help:Dummy_edit#Null_edit says
"... and the edit summary is discarded."
The user types his valuable comments into the summary box.
The save completes as if all is well. And his comments have
been thrown away without even the least warning.
He tries again. All seems to proceed well, but he is at a loss
why his summary doesn't appear anywhere. It's as if he was only
just dreaming he hit Save Page.
He concludes there must be a bug: if there is a zero difference in the
text, there must be some divison by zero causing the program to not
process his subission, but return sucessfully as if it did.
Little does he know that what he was doing was the insider's way
of purging a page, and it is even documented that his summary was to
be thrown away.
He walks away saddened that there must be a bug.
Version: unspecified
Severity: enhancement