It looks like the expectation of having empty "rebuild-only" commits is not documented anywhere. Since they are one of the benefits of rpmautospec (for easy cherry-pick-ability between branches), this seems to just be an oversight.

For example, the releng mass rebuild script now does something like this:

• rpmdev-bumpspec $PACKAGE.spec --comment $MESSAGE
• git commit -a --allow-empty -m $MESSAGE

In the rpmautospec case, rpmdev-bumpspec will not modify the .spec file, so committing with --allow-empty will just create an empty commit with the expected message, and increase the calculated release_number by 1.