Priorities don't work as expected, terrarium gets water before microbe musher even if microbe musher priority set to !!

As I understand it, the duplicant priority setting categories are considered first, then the priority of individual tasks within that category. And the life support category takes a higher priority than the supply category by default.

I follow your line of reasoning, though when something is set to highest priority should that not matter? To go with that when there was plenty of water duplicants would make mush bars, when there is a shortage water make no food? I know I have made mush too late in the game, I'm working on learning the game dynamics. It could be you are correct and this is the dynamic expected by the developers. Time will tell.