Shining - I used to puzzle over this ability to appear 'normal' to some people. My eldest son's view is 'Dad can do 'normal' for a short period but then the cracks start to show'.
Also the closer they are to people, the more obvious it is there is something wrong. Most MLCers do not have a close emotional bond or the usual sort with their parents . . if they did they probably wouldn't be in MLC.
I don't know if you have seen a fascinating study of identical twins - the closer you are to them the less likely you are to be fooled, even for a minute, whereas acquaintance and casual friends can be taken in by one posing as the other for long periods.
In other words we pick up more cues when we are close to someone. And I also agree with AJ that to some extent people see what they want to see.
Soon after my xh left me, some former friends told me he was fine and never happier, whereas when I met up with him to discuss the separation and money matters, he looked terrible, really terrible. The former friends supported my xh (the only ones that did, and interestingly they have made overtures to me in the last few years, which I have replied to politely - (I think that NOW they can see he is really crazy).
I always tell them that I am fine, and life could not be better!
