iBotPeaches is going to assassinate you. He explained this "bug" 10 times already... in different forum threads; general ones, ROM specific ones, in the bug section... and yet you ask the same question again!
I wonder - do you even read anything on this forum before posting a question? At least the bug section? Do you use the search function at all?
Anyhow, I'll explain it to you once again (and in a very short version) - designer of the MMS.apk decided to disable the landscape mode, so this is not a bug.