Why does the IPython interpreter freeze on OS X when launched with --pylab = wx?

I have a python package that uses both wxPython and matplotlib. To get non-blocking windows, I tried to start IPython like this:

# ipython --pylab=wx

      

        
        
        
      

    

When I do that, the IPython prompt appears and a wx icon appears on my OS X pane, but the IPython command line immediately freezes (I need CTRL-Z and end the process to exit). I get the same behavior if I start it with " ipython --pylab

" with the base matplotlib block set to "WX" or "WXAgg" in my matplotlibrc file.

I can start IPython with

# ipython --pylab=osx

      

        
        
        
      

    

But when I run any command that creates a wx window, I get an error stating that I need to create first wx.App

. So to get it to work, I have to start IPython in the mode osx

as above and then immediately type

In [1]: import wx

In [2]: app = wx.App()

      

        
        
        
      

    

I see this on OS X 10.6 with wx 2.9. I get the same behavior whether using Ipython + packages installed natively or via macports. I don't see this behavior when running on RHEL 6.3 with wx 2.8.12.

How can I eliminate the need for this hack and start it right?