Once you unlock the extended area in the game you can cross a meadow and go down to a solitary tree on the edge of the meadon on the right hand side.
While doing so I noted that in the water of the lake far behind the tree there was a strange reflection and as I came closer I noticed it is actually the tree itself causing a reflection in the far-away lake.
Now, by the laws of physics, this is not possible. You cannot see, in a lake, a reflection of an object that is in front of the lake. Found this very irritating.
It's only a minor glitch though.

Another minor glitch is that there is still a rain effect even when you are in the cave.