On this:

C:\>perl -v
This is perl, v5.8.4 built for MSWin32-x86-multi-thread
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both lists are sorted identically using your exact code.

Using:

$ perl -v

This is perl, v5.6.1 built for i386-linux
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the results are the same as yours. Changing the eval'd version to:

  # sort criteria eval-ed: wacky results
  my $sortCriteria = sub { $hr->{$b}->{"number"} <=> $hr->{$a}->{"numb
+er"};};
  # WHAT AM I DOING WRONG ON THE NEXT LINE?
  @sortedKeys = sort { &{$sortCriteria} } keys %$hr;
  print "\n\nsort criteria eval-ed\n";
  foreach my $sortedKey(@sortedKeys){
    print $hr->{$sortedKey}->{"number"} . " " . $hr->{$sortedKey}->{'n
+ame'} . "\n";
  }
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yields an identically sorted list, leading me to:

  # sort criteria eval-ed: wacky results
  my $sortCriteria = '$hr->{$b}->{"number"} <=> $hr->{$a}->{"number"};
+';
  # WHAT AM I DOING WRONG ON THE NEXT LINE?
  @sortedKeys = sort { &x($sortCriteria) } keys %$hr;
  print "\n\nsort criteria eval-ed\n";
  foreach my $sortedKey(@sortedKeys){
    print $hr->{$sortedKey}->{"number"} . " " . $hr->{$sortedKey}->{'n
+ame'} . "\n";
  }
  sub x {
    eval shift;
  }
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yielding the same identically sorted list but using an easily changed string.