Ghost shifting DT shifters

The cable must be going slack, it only pulls the mech to the larger cogs, it is the spring in the mech that pulls it onto the smaller cogs.

Just to make things clear, no.

The cable does not go slack, it gets TIGHTER and literally pulls the shifter back round. When on the largest sprockets the cable is obviously under the highest tension, and it is here where if I try to ride up a steep hill it downshifts.