The following test case, when run on the direct2d platform plugin, enter a state where the event loop enters the system event processing loop, but does not wake up and deliver events to the application. The only thing that seems to work is resizing the window (to a larger size) to trigger a WM_PAINT which eventually wakes the event loop.
After the window is resized, all the events which were waiting to be delivered (clicks, etc.) suddenly are.
Another related test case reveals the same behavior by creating new windows from an event filter. Holding any key will create windows continuously until the event loop blocks. Then, no new window are created until one of the windows is resized: