Well, because I think, that both spell effects have to be seen independant of each other, since they are not allowed to stack.
While it makes a difference to the spell taking effect or not, what type you currently are, it should not be that type, but rather your original type on which the spell effect is based in this case, because of the overlapping.
A similar question would be, if a human is subject to a
Hold Person spell and then transformed into a giant via a
Polymorph spell. Would the
Hold Person still hold the polymorphed human or not?
I'd say no, because the spell cannot affect giants.
Now why is that similar? On the first glance it looks like the opposite of what I'm saying.
The similarity is, that I believe the prerequisites should be met all the time (exceptions exist, of course, if a spell
itself alters the target in a way, to make its own prerequisites invalid, like the
Shillelagh spell), not just once at the beginning and then forgotten about.
Bye
Thanee