I tried to replicate your issue indeed there is no updating of the dependant start dates if you move the deadline of the first topic back; it only updates the Finish to Start''relationship when moving the deadline forward in time.
I stood in contact with the german collegues. They have a Macro for this issue. Hopefully they will implement it into the new version of mind manager 2015. For more information please ask Rainer Obesser from Mindjet Germany. in Germany they call it "kürzester Pfad.mmap"