Greetings Monks ! Have been chasing a bug in a large script, and finally distilled the issue into 3 lines. And for the life of me can't figure out what's going on. Here you go: 
use strict;
use warnings;

print grep({"" =~ /$_/} (""))."\n";

"foo" =~ /foo/;

print grep({"" =~ /$_/} (""))."\n";

[download]
Basically, there are two identical grep calls, with a regex between them. This prints (at least in ActiveState Perl 5.12.3 on XP SP3): 
1
0

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Why in the world does the "foo" regex in the middle affect the second grep result ?

In reply to grep trouble by LogMiner

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