It would appear that the build system has the git sources downloaded and tarballed so that it doesn't have to download every time the package is being built. But PKG_RELEASE is not part of the file name, and so the build system does not recognize the sources have changed and have to be downloaded again (even though PKG_SOURCE_VERSION has changed).
Change PKG_VERSION (and drop PKG_RELEASE to 1) to force build system to build from newer sources.