Be absolutely sure you aren't putting some rudder input in while doing the pitch pump. I have a bad habit of thumbing in a little bit at the extremes of collective stick. Makes it look like blowout, but in fact it is not. This is especially true for left "blow out". Blow out on a clockwise rotating main rotor is almost always to the right (nose left). Exception is if you have too much pre-compensation dialed in, as Tony mentioned.
I thought I had a similar problem until I realized I was thumbing it in. Just do a few being very mindful of any rudder input you're feeding into it. If you're sure it isn't you doing it, then check precomp settings.