mutated,
at any rate it works now

No it doesn't. I understand that you are learning and am really not trying to beat you up here but before saying something works you should verify the output against the expected results. I have only slightly modified your code, but I left in your case sensitivity mistake SEP vs sep.

#!/usr/bin/perl
use strict;
use warnings;

my @array;
while( <DATA> ) {
  @array = (@array,$_);
  if (/<sep>/) {
    print join '',sort {$a <=> $b} @array;
    print "<sep>\n";
    @array=();
  }
}
print join '',sort {$a <=> $b} @array;
__DATA__
<sep>
22
1
3
<sep>
4
2
44
[download]

Here is the output:

Argument "<sep>\n" isn't numeric in sort at foo.pl line 14, <DATA> lin
+e 8.
Argument "<sep>\n" isn't numeric in sort at foo.pl line 14, <DATA> lin
+e 8.
<sep>
<sep>
1
2
3
4
22
44
[download]

---

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