I have an application with a GUI using Pyside or PyQt (the compatibility layer is https://github.com/ros-visualization/python_qt_binding). This application displays matplotlib plots in interactive mode to avoid problems with the event loop.
It works well with matplotlib 1.3.1, but when I update to 1.4.0 the plots are not shown anymore. I tried upgrading and downgrading matplotlib only, and it confirms that the problem is linked to the update.

If I try to add show() after the plot, the window is shown with the warning QCoreApplication::exec: The event loop is already running, as if it was in non-interactive mode.

The return value of isinteractive() is 0 if I call plt.ion() and False if I cann plt.ioff().

I tried to write a minimal example of the problem but it works fine in the console. I don't recall anything special in my application that would change the behavior.

I use anaconda under Linux (Manjaro).