This patch creates new bugs.

Thanks for your information.

I have a policy of not telling Markus where the bug is,

I find this kind of response strange.

because otherwise he'll just resend the patch

This can also happen when the other contributors request it.

and I have told him many times to stop sending these cleanup patches

Software "cleanups" seem to stress the review process to some degree.

that just introduce bugs and waste maintainer time.

I guess that the situation is mixed depending on the subsystem
or concrete software module, isn't it?

Regards,
Markus