This has nothing to do with walking on the grass, frankly, and everything to do with how the Catholic Church apprehends its relationship with science.
Let's say the powers that be look around and realize a lot of people are walking on the grass. They study the Fathers, Scripture, Councils, etc., and decide that the opinions are evenly divided. So they turn to the scientists, who all inform them that it is indeed healthy for people to walk on the grass. So the Magisterium follows the scientists' findings and issues a letter or something to all the bishops, who are informed they should tell their flocks that it is indeed a fine thing to frolic on the lawn.
Years pass. The scientists study. They come to the horrifying realization that they were Dead Wrong. Walking on the grass is hazardous to one's health and ecologically a disaster, etc. It causes bug bites and so diseases are incurred and adolescent rebellion and Woodstock and the people who make "Keep Off the Grass Signs" are now unemployed, so the economic impacts are dire and profound in many ways that are irrelevant but entertaining anyway. They present the results of their studies to the Magisterium.
What does the Magisterium do, as it has already ruled? Does it reverse itself? More specifically, is it possible there are issues that are actually scientific issues that the Church has invested itself in, when it should not, because they are not issues of faith and morals but rather of science? Or because the Church says such and such is an issue of faith and morals, it then becomes one?