I'm not sure if this was an accident or not but this is exactly what is in the library now and the lines showing as deleted are what it should be. You are correct that there is an error in this function though. The correct form is as seen here: https://github.com/libgdx/libgdx/blob/master/gdx/src/com/badlogic/gdx/math/Matrix4.java#L257. If you update the pull request I'll merge it.