Ok, so I've took some time and watched the LEDs on my board while running Mach3 - btw, my board is the C1 rev10 from CNC4PC, so LEDs on all step/dir connections.
In Mach 3 all related motor LEDs are off by default. On first move, the step LED lights up regardless of direction. The direction determines whether or not the DIR LED lights up (as far as I can remember now, being late and I'm nearly an old fart). Going X+ lights up the DIR LED, while then going X- turns off the DIR LED. This behavior can be observed across Y and Z axis as well.
Now, in Mach 4, it is a similar story, but not quite. The Y axis seems to behave as it should. I disabled the other motors and then started to work through them all individually. While the Y works as expected, I'm seeing interesting results on the failing X axis. If I go X+ first, I only see the DIR LED light very dimly, as though it is getting no power. The Step LED does not light at all. However, if I then press X-, the Step DIR lights up brightly and stays lit (as I would have expected it). If I then press teh X+ again, the Step LED goes out, while the DIR LED again lights very dimly.
I stopped at X failing because this old man gots to go to bed (having started with Y because I knew I could get it to work and wanted to verify my sanity). Will conclude next evening with Z and see if there are similar results. I suspect that I have something crossed somewhere, but then again, maybe not. Mach 3 works flawlessly, so it could be a number of things. The CPU by the way stayed quite low - never over 10-15% that I remember seeing.
I saw the same results with 1-17, and with 1-18 just released today having seen it posted while I was checking for feedback - Thanks Art!
Trent