While adding or editing a forest you can assign a rating to the forest by assigning it stars. When you push on the left side of the star, that star will be selected. When you push on the right side of the same star, the next star is selected. This is a problem in Android, specifically in versions below Nougat 7.0.0(It is solved in 7.0.0).

See https://code.google.com/p/android/issues/detail?id=218475 for further details.