[NTG-context] math font definitions in XeConTeXt

Dear all, For korean sentences, I am using XeConTeXt with korean otf font as the bodyfont. In that case, greek capital letters in math mode are not displayed wit the warning message "** WARNING ** Glyph for CID 18168 missing in font "YoonMyungjoM/H". YoonMyungjoM is the name of the korean font. If I set english font as the bodyfont, they are displayed well. I think that korean font override the greek capital letters. Hence, I'd like to know the followings: (1) Is there a math font which can be used in XeConTeXt? (2) Is there a way to not to override greek capital letters in math mode? Thank you. Regards, Dalyoung