The current behavior isto set_next_input of only the line where ? is situated.
It also seem to differ from previous transformer in case of assignment and for loop:

for i in range(10):
   x = range? # set_next_input in 6.x,  not on 7.x

I'd argue that set_next_inupt should be set for the whole cell, and regardless as to whether there is x = or not as long as there is a first line.