While CM is running a program, Spacebar invokes Pause. This is a good thing.
Once paused, Spacebar invoke Emergency Stop, the machine disconnects, and you have to re-connect and Initialize.
A Poll suggest that this is not the desired behavior. People would rather that either the program resumes, or that it do nothing at all. Emergency Stop got zero votes.
There’s no code in Motion to make the spacebar trigger pause. It’s the basic keyboard navigation built into the OS, and the pause button happens to have focus when you hit the spacebar. Once the pause happens, the button is disabled, so the focus shifts to the stop button.
We can change this to make the spacebar an explicit pause, but it breaks keyboard navigation because we need to intercept all spacebar events when the “Run” window is active. Personally, I don’t think that’s a problem for a CNC machine controller, and I actually prefer it, but I guarantee we’ll get a complaint on day one.
So it sounds like that “Spacebar is Pause” is, right now, a happy accident. The problem with happy accidents is that updates can turn them into unhappy accidents.
Rather than intercepting all Spacebar events, could the program be a bit more explicit about where the focus is? I know on Windows that the focus order is quite malleable, I don’t know if Qt exposes that to the program.
The Set Zeros page also has awful focus order problems. Hitting Tab to move among the fields visits them in seemingly random order.
@mhotchin , check out the CM 657 announcement Rob and company are listening! 
- (NEW) In Run, hit space to pause. It will no longer work for other buttons and tab navigation.
I’m eager to try the improvements out myself.