As a part cuts, the display shows what has already been cut by leaving a light blue trail of dots superimposed over the toolpath display.  This has always worked in the original screens that come with a new download of Mach.

However, now the "already cut" dots are not staying on the display.  It will show for 2-3 contours usually and then reset.

Is this a bug, or is it a problem with my computer?

Anybody else out there have this problem?

I don't see it as a problem - if you get the display originally, before you start, you get a good idea that what you get is what you want.

I think there have been some alterations to the toolpath display recently, because it takes a lot of computing power, this might be one way to cut down on what is required.