How does single-step work in Qtaxis?

I wrote a short test program to try and work out how to use Qtaxis, and I can't figure it out.

I have a video here demonstrating my confusion:

Basically the single-step button never does anything. The only way I have found to single-step is to click the pause button and then repeatedly click run, but this seems to skip over some moves? For example it completely ignored my rapid move to X0Y0Z0 and went straight to X0Y0Z-5 with the G1 feed rate.

Am I missing something or is this just broken?

Cheers.

I can't run Axis because my PC doesn't boot unless I blacklist the glx module, and Axis doesn't work if it can't use OpenGL. I can only use the Qtvcp GUIs. I have ordered a replacement graphics card, hopefully that fixes the problem. In the meantime I'd like to understand how single-stepping is supposed to work in Qtaxis.

So I haven't tried it in Axis, but the G-code is not complicated:

G0 X0Y0Z0
G1 Z-5 F500
G1 X100 F1000
G1 Z0 F500
M2

I don't think the G-code is faulty.

I checked master and it seems it is broken, but you can use the run button after pausing the program.

Are you using linuxcnc 2.8 or master? I'll look into this soon.

linuxcnc's step mode does not actually step each line of GCode, it steps each line of internal motion messages, which are sometimes slightly different. motion messages sometimes combines Gcode lines.

If motion messages combine G-code lines when in single-stepping mode (it moves straight to (0,0,-5) instead of going to (0,0,0) first - wouldn't the same thing happen when I run the G-code without single-stepping?

EDIT:
If the diagonal move from the video is caused by combining several moves - does it only combine them when single-stepping and not during normal usage? I'm surprised that the behaviour would be different.

Running the code or single stepping should create the same moves, though I wonder about linuxcnc's look ahead. look ahead can modify the moves depending on the g61/g64 setting.
I don't know but maybe single stepping doesn't use the look ahead properly?
Do you set g64 to a reasonable number?

I thought G64 would be irrelevant, because in single-stepping mode it has more time to fit the prescribed path, and the deviation from the path is a dead straight line, it's not blending the corners.

However I added "G64 P0.001" to the top of my program and now it behaves in single-step mode exactly the way I expected! So it seems there might be some bug to do with lookahead in single-step mode?

There is still the problem that the single-step button doesn't work and I have to single-step using the Run button in Pause mode.

(Also, less importantly: when I take it out of Pause mode I get a popup saying the program ended without a percent sign or program end, but the program does end with M2).