Ah. I see what's happening. The "Auto Reload" function must allow monitoring of any change in the external file and recompiling (well, re-interpreting anyway) the code as soon as it is saved back to disk.
(Edit: The OpenJsCad program doesn't render OME's screwthread file (.scad) properly. Not good news there)
(Edit: This "Auto Reload" isn't functioning i as expected. It seems to be constantly reloading/re-rendering the file. Think i'll stick to using the "Reload" button)