I would posit that this is not a bug, but working as intended. You really don't want more than one person working on a sheet at once, and if you do have multiple people working on it, you want them doing so in their own instance of it. Let's say I'm working on a change, and so is GM-A, if I save, GM-A's work is invalid, and if he then saves, my work is deleted. Why the API management is available to co-GM's is a bit beyond me, but it is just script work. If you mess it up, it just stops working, go back and fix or remove. If someone is tinkering with your carefully crafted sheet and deletes a vital attribute, it could be days to figure out what went wrong where and fix it in larger sheets and even then, there could be a myriad of other issues by then if the person keeps making changes.