Cubemap Face size is not restoring texture quality to the original texture's quality.

When the cubemap face size dropdown is changed to a lower resolution and back to the original, the image quality for the cubemap faces is getting worse.

Repro:
1. Create a New Cubemap and assign a texture to all six faces
2. change the cubemap's face size to a lower resolution, 16, than the default 64
3. Change the Face Size back to the default 64
(optional: repeat steps 2 and 3)

Result:
The faces' image quality is getting worse when Face Size is changed back to 64 from 16.

Workaround:
Reassign all textures to the texture slots.

Note:
An assert is also thrown from the object picker when trying to assign a new texture to the cubemap faces. See related case 400831.