member_id and member_member_register

i have gotten the blessing from lisa to copy EE code from mod.member_register.php to my redirector extension.

so far it is going well. hooking at member_member_register does the redirection after registration. however, when it gets to the point to update the existing active session variables, specifically $member_id, is not available to my extension even though i was extending Member_register.

but if i change the hook to member_member_register_start, and copy all the required code between the 2 hooks, $member_id becomes available as it should.

what i dont understand is that i dont see any redeclarations or reassignments of $member_id and yet it somehow has been unset. this could be the fact that i am an OO noob, but then why does it work from member_member_register_start ?

anyone muck around with this before ? thanks in advance.