1.8.0.10

I am not using any mods at all

Previously before the 1.8 Update i could make preview images at 400x300 perfectly fine without any problems, when i decided to try and do it today i found that the target resolution has been locked to 1600x1200 and i cant find a way to change it back, when i try making a preview image at that resolution the outcome is an extremely blurry and out of focus image. Tried with and without the _BCR suffix and it didn't make a difference.