According to man page, -n option should exclude spf1 policies for PRA checks, but it doesn't do that.
The attached patch fixes that beside improving the way PRA policy gets selected.
I think it could be improved by doing rcount-- just after memset. I also think that memset and rcount-- should be performed on all TXT records that are not valid SID/SPF policies.
sid-milter-1.0.0-nopra_on_spf1.patch