When using set_ylabel('Täst') in the ipython notebook, there will not be any plot, but also no error message visible. The real problem is that the notebook does not show exceptions that happen in draw(), but also in the console ipython, an exception raised by set_ylabel() itself would be rendered much better than the one coming asynchroneously from draw().

If possible, an exception like this one:

  File "/usr/lib/pymodules/python2.7/matplotlib/cbook.py", line 1797, in is_math_text
    "matplotlib display text must have all code points < 128 or use "
ValueError: matplotlib display text must have all code points < 128 or use Unicode strings

should already be raised in the Text() constructor (or whereever appropriate).