While I don't think iRacing is nearly as realistic as it should be, this behavior isn't that strange or magic. To some extend, the engine power cancels out the braking that is done at the rear. Say this is achieved perfectly, then you have a 100% front brake bias, with free rolling rear tires.
The front tires are locked, so regardless of steering, they produce contact patch force perfectly in the opposite direction the car is traveling. Even at 25 degrees car yaw angle, the front tire force is mainly longitudinal (braking). Rear tires purely rolling produce virtually only lateral (cornering) force.
Which way will the car turn? Well its kinda simplified but calculate the torque each tire grip puts around the car center of gravity. Both the rear tires produce lateral force, which both create great rotation potential. The front tires create less yaw torque around the car center of gravity because they are braking more than turning. Result? The car will straighten out.
The results will vary a lot because in each gear, you change the driving torque at the rear wheels yet the braking torque is the same maximum in each gear. I guess in 6th gear, you can't keep the rear wheels from locking up and the car will rotate more and possibly spin out. In 1st gear at low speed, perhaps the driving torque is much greater than the braking torque, so you still get big wheelspin, which acts kinda the same as a locked tire (no lateral grip), so you may spin out too.
It is likely to work in quite a few cars in quite a few sims. The only "bug" is us, self proclaimed simracers approaching it like a game, doing things you would never do in real life... I needed a gamepad to try this out as I can't get my feet to do this, even in a simulator!
Can't tell you how much bribing my friends have to do to get me to play an epic game like Battlefield 
