See the example below. All branches end with a stop. However, there is a strange line added below the graph. It seems that it assumes that at least one path has to continue to the end. If the nested decision is removed and only two branches of one decision end with a stop each, the graph is drawn correctly.
start
if (a) then (yes)
:asdf;
stop
else
if (b) then (yes)
:asdf;
stop
else (no)
:asdf;
stop
endif
endif