Headscarfs and veils with respect to trans-gender-people?

It is my understanding that female humans obeying the muslim religion must (or choose to) hide their hair and sometimes even face from non-family males. However, it is well known today, that 1. the biological sex is not at all binary, meaning that some individuals cannot be clearly identified as either biologically male or female (not even by looking at their genitalia) and 2. the gender identity of a person must not necessarily match their biological sex, meaning a biological male can feel, clothe and appear in a feminine way (or the other way around). How does the previously mentioned rule (if I did not misconceive it) address this circumstance? For example, does a [cis-woman](http://en.wikipedia.org/wiki/Cisgender) adhering to the tenets of islam, * have to veil herself in the present of a non-family trans-male (a biological woman, with a male gender identity)? * Or would she have to veil herself in the presence of a trans-female (a biological man, with a female gender identity)? Which is particularly problematic, as the person would be almost impossible to identify for the muslim woman. * Or in the presence of a non-gender person without a clear biological sex? * And finally, what about post-surgery trans-persons (i.e. after surgically changing their physiological features and genitalia)? ---- *Note: I don't know the attitude of islam towards its members being trans (that would be a different question), but given that muslim individuals may interact with non-muslims they may still encounter trans-people.*