In src/engine-gpg.c , in the function export_common, there's this snippet:
if ((mode & GPGME_EXPORT_MODE_MINIMAL))
{
if ((mode & GPGME_EXPORT_MODE_NOUID))
err = add_arg (gpg, "--export-options=export-minimal,export-drop-uids");
else
err = add_arg (gpg, "--export-options=export-minimal");
}However, recent versions of gnupg require --export-options=export-minimal,no-export-attributes to drop the uid.
I don't know how to add compatibility with older GPG versions to gpgme, but if that is not needed the fix is simple of course.