Spyder plotting blocks console commands
I was having a similar (I think) problem.  Make sure your interpreter is set to execute in the current interpreter (default, should allow for interactive plotting).  If it's set to execute in a new dedicated python interpreter make sure that interact with the python interpreter after execution is selected.  This solved the problem for me.
Whenever I execute a plt.show() in an Ipython console in spyderlib, the console freezes until I close the figure window.  This only occurs in spyderlib and the blocking does occur when I run ipython --pylab or run ipython normally and call plt.ion() before plotting.  I've tried using plt.draw(), but nothing happens with that command.
plt.ion() works for ipython, but when I run the same command in spyder it seems to not plot anything altogether (plt.show() no longer works).
Enviroment Details:
Python 2.6.5, Qt 4.6.2, PyQt4 (API v2) 4.7.2 on Linux