If you don't specify it on the m//, s/// or qr// that builds a regexp, ^ and $ will act as if you didn't specify it. Absence of "m" does not mean "inherit". For that reason, qr// without "m" turns off the option for the regexp it builds.

>perl -le"print qr/foo/"
(?-xism:foo)

>perl -le"print qr/foo/m"
(?m-xis:foo)
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Until very recently, there was a bug that caused (?-m:...) to be ignored in some circumstances.

>perl588 -le"$re=qr/a$/; print $re; print qq{a\nb\n}=~/$re/m ?1:0"
(?-xism:foo$)
1

>perl5100 -le"$re=qr/a$/; print $re; print qq{a\nb\n}=~/$re/m ?1:0"
(?-xism:foo$)
0
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