@DoubleDown First, to the statement "the motor locked up": this is a common misinterpretation of the OW giving 100% but being asked more than 100% which allows (not causes) the board to tilt forward. Bar some severe defect that would occur at any speed, the board does not "lock" under stress. Bonks are a function of this. By putting the board under stress then deweighting, the motor continues to give 100%, springing the board upward along side the effects of bounce. Without the deweight a bonk would be a nosedive. Seeing as you were using a high level of acceleration at said speed you should have nosedived so I'll just operate under the assumption of a typical nosedive. Why is simply a function of acceleration. As glyph said, use gentle acceleration (and of course don't hit any bumps, go uphill into the wind etc).
Have you ever asked yourself how pushback works? Think about how the OW keeps your nose up under normal circumstances. It is simply an effect of acceleration. As the board accelerates and moves faster than your body, two things happen. A: Your position in relation to the OW changes and re-centers you. B: The force applied by the motor to roll the tire forward has an equal and opposite reaction on the board, which forces it to twist in the opposite direction, lifting the nose and pulling the tail down. When pushback occurs, generous leeway must be present in the board's capacity to accelerate. If it is not, the board will slam on the gas (in addition to you already slamming on the gas) and actually take part in causing the nosedive itself. Also, your acceleration can mask the pushback and cause it to become weakened or unnoticeable. Pushback cannot assist in acceleration based nosedives, those that are caused by the environment or battery. It will only help if your speed is the ONLY problem.
The auditory warning may not work as well for the OW as many may believe. The idea sounds great if we relate the OW to the EUC. The EUC has much more leeway than we do. Because it does not suffer from the lever effect, the battery doesn't become noticeably weakened as quickly nor does it nosedive as easily. The auditory alarm could be set to 15 mph in an attempt to precede nosedives and even then, it wouldn't always. We are always much closer to the limit on a OW than we think we are. The beep would have to occur much earlier and more often than that of an EUC (the frequency of which would have to parallel the difference in nosedive frequency between the OW and EUC, which is massive), would become a nuisance, and would likely cost FM money. I used to think that would be a good idea but let's be honest, the air around the OW would sour as this machine becomes associated, not only with nosedives, but also with constant, nonstop beeping.
If software were written to turn the board completely off, 99.9% of us would nosedive 100% of the time when said limits were reached, causing more nosedives than are already happening. Offroad rides would become virtually impossible, killing at every bump. Bonks will become a thing of the past, throwing us off instead of launching us into the air. The board continues to give 100% till the last moment because that is the best chance of survival for the VAST majority of us.
Yes, FM's massive ad campaign has probably given many new riders the wrong impression about this board. If you want speed, you still want an electric skateboard. They have done a top notch job designing this rideable and there's not much more they can do at this point. The OW is king of 180s, 360s, bonks, drops, burnouts and pretty damn solid for carving. Going over 15 mph is still "sniping with a shotgun". If you want to snipe, the tool you will need is a sniper rifle, not this shotgun.