If you assign a random LFO to the arpeggiator it becomes impossible to set the midpoint of the moulastion with the rate control since it shows the modulated value.
Reproduction path:
1) Set LFO to random wave and speed 1/16
2) Assign lfo to arp rate in the mod matrix and set modulation depth to 50.0
3) Try to change the arp rate; the values will jump around while doing so.