TinkerGnome turning off heater after a few secs when sent command from computer controller

[JRDM 5]

I use Simplify3D's machine controller from a computer and I find that the UM2 automatically turns off the heater a few seconds after I try to set a temperature. Is there a way to adjust this behavior? I'm using the latest but this behavior seems to have been like this for the past couple years too.

[halfie 8]

I'm noticing this too, particularly through Pronterface. I'll set the temp to 185, and it'll either stay there until it hits 185 and then immediately turn off the heater, or stay on for a few seconds and turn off. 

 

Looking at the printer, it seems as if it's going into the preheat menu for a split second and then leaving it.