Bug. This is fixed between 5.6.1 and 5.8.0: Compare:

$ perl -e '"foo" =~ /(o)/; print @+,$/'
22
$ perl -e '"foo" =~ /(o)/; print "@+",$/'
@+
$ perl -v
This is perl, v5.6.1 built for i686-linux
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..to:

$ perl -e '"foo" =~ /(o)/; print @+,$/'
22
$ perl -e '"foo" =~ /(o)/; print "@+",$/'
2 2
$ perl -v
This is perl, v5.8.0 built for i386-linux-thread-multi
[download]

perl -pe '"I lo*`+$^X$\"$]!$/"=~m%(.*)%s;$_=$1;y^`+*^e v^#$&V"+@( NO CARRIER'