awk oddity: 2.8BSD vs. ULTRIX

[Jeffrey W Percival]

Here's a curiosity I hope someone can help me on.
I have a file called "cmd" with this line:

    { $1 = $2 + $3 } { print $0 }

and a file called "data" with this line:

    1 1 1 1

When I type this command:

    awk -f cmd data

I get these responses:

    2 1 1 1                 on 2.8BSD on an 11/70

and

    1 1 1 1                 on ULTRIX 32m v. 1.1 on a MicroVax II
                            and on 4.2BSD on a Vax 780.

Why does awk vary in its response?
-- 
	Jeff Percival ...!uwvax!uwmacc!sal70!jwp or ...!uwmacc!jwp