Positioning Nodes With `{rank=same ...}` Side Effects

There is no hidden semantic meaning in rank=same, this is simply a bug.

The edge is correctly drawn when for example omitting the label of the edge or rankdir=LR.

You may correct this particular graph by adding the dir attribute to the incorrectly drawn edge:

q3->q4[label="λ", dir=back]

This is of course of no help when dynamically creating graphs.

This bug may be related to one of the other known bugs caused by rankdir=LR, reported on http://www.graphviz.org:8080/bugs/openbugs.html