Changing zero point with UCCNC (USB100) - 800/2

Hi,

i'm still a newbie, but i'm making progression, if it wasn't for this hatefully fact that all of a sudden, the zero point of my 'masterpiece' is changed by the stepcraft or the UCCNC software.

Here's a Porsche woodcarving that i was making for a couple of hours and then suddenly, at 1/4 of the end, the zero point is changed by some 20 mm.
i noticed that the speed by which the x-axis is travelling changes too during this moments, resulting in breaking the mills.

It has nothing to do with grouped or combined toolpaths, since only 1 toolpath is made in Aspire and exported as a Mach 3 file.

Who can help me with this horrific error, which ruins all of my workpieces.