Text randomly disappears while typing? rMBP OS X 10.8 Mountain Lion

While chatting with friends on facebook, the text randomly disappears and appears at random intervals. I cannot induce the effect manually. It is very frustrating to see the text suddenly disappear yet show when I press enter.

Is there a specific reason ? Maybe spelling autocheck or autocorrect ?

EDIT

Any updates on this ?? Is there a fix ?
I'm experiencing the same thing — there appears to be a rendering bug in Safari. Sometimes I see visual glitches when scrolling, too. It will probably be fixed in a software update in the future.