What Multimeter reading?
Most likely here is what is happening. 

The fuse for the mA circuit in your meter is blown and that is why it is not making a connection with the red lead in the mA plug. 

With the lead of the meter in the 20A plug, only when the dial is set to A do you get a valid reading. With the red lead in the 20A plug and the dial set to mA the reading that you see is just noise, not a valid reading.