I ran into this curious situation where there was more information given by a letter being in a yellow square than if it were in a green one.

I got one green letter and two of the same letter that were both both in yellow squares. This told me that the two yellow letters had to be in the remaining two squares. If one of the yellow squares had been green instead, I would know where the green letter goes, but there would have been two possibilities as to where the other one goes.