Another slow pitch question

[walkerbard]

A few years ago I had an illegal pitch called
againsed me in a slow pitch softball playoff
game that, if I interpret the rules correctly,
shouldn't have been called. Upon reading the
rules on pitching (ASA slow pitch) I discovered
(or so I thought) that the pitcher DOESN'T
have to step TOWARDS home plate while releasing
the ball. I decided to incorporate a pitch
that I released while stepping BACKWARDS
(keeping contact with the rubber) into my
repertoire. I used it about 3 times a game
for a few games with good results and no
warnings. Then, in a playoff game, the plate
Ump calls it an illegal pitch. He said that
it "would be legal if I threw ALL my pitches
like that but since I started the game stepping
forward it would be considered deception and
therefore was illegal." Was that a correct call?
(I haven't played slow pitch since so I haven't
needed to resolve this issue until now)