If I run the example program test-multi-actions.py which comes with the upstream source code of notify-python (in tests/ directory) no notification bubble shows. If I comment out all the "n.add_action()" calls the bubble shows in the lower right corner screen, but naturally without links for the actions.
Same also with my own little test program test.py. Here an empty bubble shows up for less than a second when the "n.add_action()" call is not commented out. With the call commented out the bubble shows near the upper right corner of the screen.
The real life problem is with hal-cups-utils and system-config-printer. hal-cups-utils gets triggered by HAL when a USB printer is plugged. Then it creates a print queue and sends notification requests to the system-config-printer-applet. The applet is supposed to show a bubble via notify-python and by clicking links in this bubble the user can configure options for his new print queue. Due to the bug with add_action() the bubble does not show.
The bug is in libnotify itself, not the Python bindings. The test case there hangs, too.