NC latching emergency stop buttons are an industry standard, I can't imagine that not being supported. Plus it works well once booted.
My suspicion is that the same pin is used for something else during boot and this prevents the boot-up from completing if it is tied to ground. Does anybody have an idea?

I've spent half of each day of the past 4 years helping people with Smoothie via email/forum/whatever, and a lot of people tell me in detail what their expectations for the system are. I can tell you that there are literally hundreds of features that one person or another « can not imagine not being supported ». And everyone thinks their feature is more important than everybody else's. It's just how people are.

We work very hard on implementing everything we can implement as soon/fast as we can. Whatever you want us to have, we'll have it as soon as humanly possible. In the meantime, the system is what it is.

About your problem : I do believe that pin is indeed used to enter DFU mode if pressed at boot time. This is why pins are configurable in Smoothie : you can simply just use any other pin for this. Can you try configuring another kill pin and see if it solves your problem ?

Cheers.

Thank you for this information, it sounds like a very likely explanation :)
I will try it and if I solve the problem, I will try to add the info to the wiki.
Have a lovely Sunday.

Already added to the wiki, if it doesn't work tell me so I can remove/fix it.

I tried connecting the kill button to 1.31 and it now works flawlessly. The edit you made to the wiki is just what needed to know :)
Thank you very much for all the help!