The instructions suggest you press the momentary button while the conveyer (belt) is running. What happens if you momentarily activate "eject" with "belt" ON?
I couldn't find a video of this particular version but I was hoping to hear some kind of click or similar indication of a mechanical "gate" letting one and only one can thru for each momentary press.
I found this well-done video on youtube which suggests the eject is a separate mechanical operation and should not speed up the conveyer as is apparently the situation. Contrary to the instructions, in this example the belt is disabled between each ejection cycle.