75 cent swing from two different brokers selling the same stock at market open. Is this normal?

I set up two sales of the same stock I have in two different major brokers. Both were entered a few nights ago well before market open at 9:30AM.

For one, I sold 30 shares at $X, the other, I sold 10 at $(X + 0.75). Is this expected? For the volume of the stock, I wouldn't expect either one of my small sales to tilt the scales, so it's a little puzzling that 'best execution' at one broker would be that far off from another.