Issue 1:
  
1) Bring your cursor over a node, e.g. "Kill the Dragon" without clicking!
2) Now try to drag it straight downwards (fast and straight!). It seems that nodes only(!) move when they are at one point also moved on the x axis, otherwise when trying to move them up or down initially they keep standing still. I tested this in chrome and ff on linux. If you cannot reproduce it on the first drag, please go to another node and try dragging it straight downwards (or alternatively upwards)

Issue 2:

After dragging a node far to the outside, move the canvas (viewport). The node you just moved will start swirling around again even though it is "fixed".

Issue 3:

1) Please go to a node in the jsbin (the actual code).
2) Remove x and y specification from one of the json node objects (JSON). But leave (!) the "fixed" property.
3) Reload the bin and you'll get a "too much recursion" error (console).