A long time ago, back in 2012, I reported the presence of erroneous behavior in PlanMaker. Unfortunately, I have to admit that even in the PlanMaker 2021 version, this problem has not been solved. As proof, I'm attaching a picture that reproduces the problem.
The picture is animated.
Note the unwanted change to cell B3!

https://mega.nz/file/3653HbLL#2NMQN5eh1 ... abWiLkvtEw