Looks like a perl bug to me.... If you flatten out the while() loop: 
#!/usr/bin/perl -w
use strict;

$_ = "abc def\n";
/^(\w+)\s+(\w+)$/;
print "<$1><$2>\n";

$_ = "xyz 6-7\n";
/^(\w+)\s+(\w+)$/;
print "<$1><$2>\n";

$_ = "123 456\n";
/^(\w+)\s+(\w+)$/;
print "<$1><$2>\n";

[download]
The output is 
<abc><def>
<abc><def>
<123><456>

[download]
Which is what the expected output of your snippet should be. FWIW, replacing the while(<DATA>) with a for(@data) type construct, also producted erroneous results.

Before using $1 et all, you really should check to be sure your match succeeded: 

while (<DATA>) {
  if (/^(\w+)\s+(\w+)$/) {
    print "<$1><$2>\n";
  } else  {
    print "Line $. didn't match\n";
  }
}

[download]

-Blake

In reply to Re: partial results in $1 $2 after re failure by blakem
in thread partial results in $1 $2 after re failure by Anonymous Monk

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