Set individual motor speed via serial commands while using mixed mode for pulse

Hello,

I am using an MDC2460 to control a differential steered vehicle using closed loop speed control.
I selected mixed mode 1 for easy steering with a remote in pulse mode.
Now, I would like to set the individual motor speeds when in serial mode. I am pretty sure this worked fine in firmware version 1.8, but I recently updated to version 2.0 and now the !S command sets the speed for channel 1 and steering for channel 2, instead of the speed of the individual motors.

I could not find anything about this change in the readme that came with the new firmware.
Also, I did not revert to version 1.8 to verify that the behaviour was indeed as described above, as the website clearly says: "Do not revert to earlier firmware after upgrading to v2.0.".

Is this the intended behaviour of the !S command in mixed mode?
Is there another way of setting individual motor speeds via serial command while using the mixed mode setting for pulse mode?

Thanks!

Some clarification of the commands I send, with the desired and actual behaviour.

Commands sent:
!S 1 100
!S 2 0

Desired behaviour:
Motor 1: 100 RPM
Motor 2: 0 RPM

Actual behaviour:
Motor 1: 100 RPM
Motor 2: 100 RPM