When switching (shunting) cars and making pickups and setouts it is necessary to move the cars around without brakes being on. In the software, the brakes are set on all loose consists and they cannot be moved without hooking up brake hoses and either 1) waiting for the airlines to charge or 2) hitting the Shift/ key (question mark) to initialize the brakes. This is unprototypical, by the way. More on that later.
The bug is that the "?" key stops working and the brakes become sticky after some time of operation. In the attched log of my Escondid Local Steam activity the InitializeBrakesCommand last worked at 09:23:52.75. Subsequent attempts to use the command were ignored by the software. This fail to function occurs whenever I am running a switch job - my most common activity - on any and all routes with all equipment. It has been discussed before on Elvas Tower, most recently in this thread: http://www.elvastower.com/forums/index.php?/topic/25416-initialize-air-brakes/page__pid__165062#entry165062. The only way to make it work again is to save and return to the activity. Then it will work for a while before it quits again. As mentioned in the ET thread, this problem was there in the software when I started using OR regularly with build 2422 in August.
As mentioned above, the operation of the brakes on loose consists and connect/reconnect operations is unprototypical. With loose consists there should be no air on the cars and the handbrakes should be set. You should be able to pick up any loose consist or any one or more wagons by coupling to them and releasing handbrakes then move them around, switch them into your train or whatever, without ever hooking up the airhoses. Hooking up and pumping up is the last thing you do after you have your train together and are ready to proceed. And when you hook up to cars with air on them, like going back to your original train with a car you have picked up, the brakes should not go into emergency. In the sim you lose all of your trainline air when hooking up and that should not occur.
If the IntializBrakesCommand worked all the time then this unprototypical action can be worked around but since it won't it has become a serious drawback to operation.
As described in the ET topic, this problem has been around for at least 6 months.
A further feature of this bug: if you continue shunting with the non-working ?-command then using this key causes the brakes to be disconnected somewhere in the middle of the consist and the handbrakes in the disconnected part are applied. This is evident when the \-command is used.