The ContinuousEventTimeTrigger registers a timer when elements arrive. The timers might be registered past the end of the window. In this case, the window is cleaned up and doesn't fire at all. That is certainly not what users have in mind when they use the custom trigger.
I proposed to let it behave like a normal EventTimeTrigger in addition to its continuous firing capabilities. So it should fire at the end of the window regardless of timers set.