Terrain Height Map Max Resolution is 4096?

There are many questions/answers that reveal Unity terrain should always be a power of 2 + 1, so I am confused why when I attempt to load a 4097x4097 height map in Unity 4.5, it responds with an error that maps above 4096x4096 are not supported. Has Unity moved to a power of 2 (no +1) that anyone is aware of? Or maybe a bug? I've seen some comments saying that a height map of 4097x4097 has worked in the past (and one person said they loaded an 8K map once). Just looking for anyone else that maybe has experienced this lately.