Input event may not be delivered after the current frame has been processed due to the following scenario:

1. Pulse N starts
2. User generates an input event
3. Scene calls mouseHandler.pulse() and schedules a task to run pickProcess
4. Pulse N finishes
5. pickProcess starts
6. the pulse timer expires and schedules a new pulse task
7. pickProcess finishes
8. Pulse N+1 starts
...

The pending input event from 2. will not be delivered after 7. because the pulse task has a higher priority (on Windows at least).
The 3D team has a demo in which pickProcess time is long enough to guarantee that the pulse timer expires at least once.
In that case the pending event may not be delivered at all.