Graphic bug

hi Mojang, I can contact you about a problem spelling very unpleasant, so when I turn the mipmap level I have all the texture disappears suddenly

I'm on my windows 64 bit java version and Version 7 Update 51 and my hardware configuration, amd phenom 2 x4, 10 GB Ram, 2 ati radeon hd 4870 in crossfire

Thank you to you good day
Cordially Johann