Why can't I set my rendertexture's wrap mode to repeat?

Hey all,
I’m trying to make a 1920x1080 rendertexture with a repeat wrap mode. However, once I change the resolution I can no longer set it to repeat; the option is there, but clicking it just does nothing. Any ideas why? I am using Unity 4.6.0b20 (which I’m locked into for the time being).

It appears that the repeat wrap mode can only be used when both the width and height are a power of two. 1024x1024 works, 1024x512 works, 1920x1080 does not, 1920x1920 does not.