I can't tell from the service manual, but in other cars I have worked on, there is a check valve at or near the nozzle (maybe integrated into the nozzle for the Honda?) which is more or less just a spring loaded ball bearing which opens when you have fluid pressure on it, then closes when you don't (so that the line doesn't drain back into the resevoir) - they usually get stuck closed, but maybe there is one and some debris is getting it stuck open?
It usually happens to dark colored Odyssey's.........seriously. When the sun hits the van, the fluid gets warmer in the rear wind deflector. As it gets warm it expands in volume and the only way out is the spray nozzle.
It is very annoying in the summer time.