git range-diff picky about passed ranges

Hello,

taking the Linux repository (with stable) as an example[1]. Commit 24906a41eecb73d51974ade0847c21e429beec60 was backported to stable/linux-5.3.y. Using git version 2.25.1 (as provided by Debian) and 2.26-rc0 (built from junio/master).

To compare these I'd like to use the rev^! syntax with git range-diff, but range-diff refuses:

	$ git range-diff dc5ae31afbae83038dfce8d2bd35bbe7ba05a536^!  24906a41eecb73d51974ade0847c21e429beec60^!
	fatal: no .. in range: 'dc5ae31afbae83038dfce8d2bd35bbe7ba05a536^!'

I would expect this command to give the same output as

	c1=dc5ae31afbae83038dfce8d2bd35bbe7ba05a536
	c2=24906a41eecb73d51974ade0847c21e429beec60
	git range-diff $c1^..$c1 $c2^..$c2

. After all, $c1^! is supposed to be equivalent to $c1^..$c1 (at least for commits with exactly on parent as is the case here).

Best regards Uwe

[1] so suitable remotes are:

	git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
	git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux-stable.git