Simultaneous movement in several axes

Hi all! I'm building a 3D printer where the A-axis drives the extruder. I encountered such a problem, if the movement is without the A axis, then the program is executed correctly, but if the A axis is used during the movement, then the speed graph changes shape and the movement becomes small jerks. Equipment used: X86 PC, MECA 7I92, stepper drivers and stepper motors. What I tried to change: computer, set high speed/acceleration of the A axis, type of the A axis linear/rotary, change the A axis to the U axis, set a very small step scale. But I didn't succeed.I took X-axis motion waveforms with and without an extruder and I don't understand why they are different?In this case, the use / non-use of the Y and Z axes does not affect the speed / acceleration of movement.

Thanks for the link Aciera. It's a pity that the motion planner is designed this way, as linuxcnc is otherwise very interesting software. Replacing the extruder axis with the Z axis will not work in my case, because my printer works on non-linear surfaces. I hope this bug will be fixed in the future. Are there any other CNC systems that work with MESA 7I92 cards?