Just to be clear, when I say stopped below, I mean the motors are disabled, bed heater is turned off, extrude heater is turned off, program execution is halted, everything is reset as if the printer was just connected to the computer.
I am running Simplify3D Versions 4.1.2 and 5.1.2 on the same computer, printer (with the most updated firmware they offer for it), USB connection, mouse, keyboard, ...., you get the idea. The ONLY change on my end is the software. Whatever codes or other program sequences that were output from Simplify3D in version 4.1.2 stopped my machine when I clicked on the E-Stop button. The codes or program output from Version 5.1.2 do not stop my machine. If the version of Marlin I have does not support the M112 command, then Simplify3D found a way to stop the machine without it in Version 4.1.2 and took that away in the current Version. I'm only asking that I get the same program output from Version 5.1.2 that I get from 4.1.2 so my machine will stop when I need it to stop. It could be that you have very few mentions of this because people have not needed or tested the E-Stop yet. You might hear more when they NEED to stop the machine because of a trapped hand or some other emergency and the button does not work.