I have a new Shopsabre IS510 with a Wincnc controller and I was experiencing some unexpected movement, even to the point of crashing into the end of the machine and into the table (soft limits didn't stop it). Luckily nothing seems to be damaged. I was using Autodesk Fusion 360's generic wincnc post processor and I noticed that it adds a G28 command at the end of the file. Its not really a big deal when running the code as at the end it just homes it self again. However, when simulating the code with a G28 command in it, it doesn't move, as its in simulation mode, but it resets the machine home position to wherever you happen to be at the time and if you then run the code it behaves accordingly. Also, it doesn't show on the axis readouts that it has reset until you start to jog an axis or command any other kind of movement. I'm not sure why a command run in simulation mode would have an impact on the function of the machine but it does and I'm sure as more people use Fusion 360 they will experience the same thing as simulation is a common thing to use. It took some time to figure out what was going on but I was able to get the machine to work properly by removing it and then repeat the error by adding the G28 command at the end of the code. I've since removed any mention of G28 in my post processor which now generates code without a G28 at the end of it but I'm sure others will have the same problem with potentially dangerous results. I've informed WinCNC and Shopsabre, maybe they will have a fix but in the meantime, make sure there is no G28 command in your Gcode if you are going to simulate your program, or anytime really as there is no need to home the machine if its already been homed.