I confirm that dragbug.py (2009-08-17!) is failing for me, almost ten years later.  I'm using Python 3.6.1/win32 on Windows 10.

This is really disappointing, because I have students who I'm teaching Python to via turtle, and I like to show them Python working.

I have found a workaround which -- if this bug won't be fixed -- I propose mentioning in the documentation.

The work-around is something like this:

g = {"X": 0, "Y": 0}

def goto_later(x, y): g["X"] = x; g["Y"] = y

def ontick():
    goto(g["X"], g["Y"])
    ontimer(ontick, 10)

ondrag(goto_later)
ontimer(ontick, 10)

That way, there is no opening for recursion within the handler for the ondrag event.