Most washing machines dilute down the bleach/softener/soap when adding it to the load. It helps with not causing the bleach to cause burn spots as if poured directly on the cloths.
In a unit we have here in our house, the bleach and softener dispensers have fill lines for liquid that you should not pass. This is because it uses a siphon effect to pull the liquid out. It is effective because there are no moving parts. I hope it is ok to post links on here pointing to another repair page!
Check this out for some images of what I am talking about and how it works. I didn't want to copy what they already put work into and claim it as my own.
I have a feeling that after the 3rd stage, the water splashes into - or leaks into the bleach/softener dispensers, and fills them up to around the 1st stage level which is below the level needed for the siphon effect to happen.
I would say it is a leaky selector valve/solenoid controlling the flow to those dispensers and probably is continually filling them during the cycles.
If you use them once in a blue moon, I would say to just empty them out, and put your bleach or softener in them. It might not add the bleach or softener at the designated portion of the cycle, but if it is bleach you are using, normally I believe that is the first thing added anyways.
That is what I think is going on.