Aha! Thanks for pointing out the use of lt vs. <. I've noticed it was odd before, but didn't pause to think about what the consequences are. There is another similar loop earlier in the script that looks like this:

    while (length($extnum) lt $numlength) {
        $extnum = "0" . $extnum;
    }
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where $numlength can potentially be set to 4. Again, $extnum is unlikely to be a very long string, so this doesn't seem to be the culprit either, but I'll have to comb through the script again to see if other abuses of lt could have caused the bug.

Thanks for the prompt reply!