GUITexture dimensions constrained to Power of 2?

I have a GUITexture I'm using as the needle for a compass to show the player's current orientation. The GUITexture was originally 32x32 but I resized it to 33x33 so there is an exact, 1-pixel center position (at 17,17 of the texture).

I have reimported it several times, closed Unity and emptied the trash, but the texture always says it's 32x32 in the editor. I have set the PixelInset to 33x33 and even when I click Open from the editor, it also shows at 33x33. But it still appears as 32x32 when it's rendered in Unity.

Is Unity auto-resizing textures to powers of 2? If not, how do I get the dimensions to display exactly as 33x33?