Well, I certainly am glad I just picked up the new Camel book. I had been having quite a time trying to find patterns common to multiple strings. I had sample input of two strings "ABCD". For each 1,2,3 and 4 character substring there should have been 2 matches, right? Not so. My original code looked liked this (relevant part only):
$all{$str} += $packets[$_] =~ /$str/g;
When I ran it against the sample input, I got weird output. For example, two character substring matches: Any combination would produce the weird 2,0,2,0, etc pattern of matching.
Following much frenzied thumbing through the Camel, I ran across almost an offhand mention to pos. I added the line
pos $_ = 0; after the previous line, and now the counts work perfectly.
I feel good that I managed to find this one by reading the FM, but also feel that I should mention it since it never came up in any of the (wonderful!) responses I've received to the pattern matching problem and its revisit.

In reply to Shot myself in the foot with a pos by Guildenstern

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