Hi all! The QT backend (backend_qt.py) does not enter QT's event loop when multiple figures were created. It works fine with a single figure though. I have tested this with Suse Linux 10.2. matplotlib.__version__ : 0.90.1 I have attached a little test program that illustrates the bug: When this program is run, two windows will appear for a split second, and the program finishes immediately. When lines 10 and 11 are commented out, the program works as expected: One window with a figure appears, and the program finishes when the window is closed. The attached patch fixes this bug. It is against the current HEAD in trunk. >From reading the code, the exact same fix should be done in the QT4 backend. Regards, Eike.