Brake lever sinks when shifting transmission

Occasionally, but not always, the handlebar brake lever sinks almost to the bar. This only happens after shifting transmission between High, Neutral, and Reverse. If I reapply the brake it returns to normal. Otherwise brakes behave correctly. Not spongy otherwise, no leaks, no loss of brake fluid. This is on a new 570 L Max.

Normal, or, malfunction?

Thanks for any feedback.