if_tap(4) being inconsistent between svn updates

I track -CURRENT (mostly for bhyve) and have found between updates that
if_tap often requires different calling semantics to work... sometimes it
needs and IP ad sometimes it doesn't it s the primary problem (on the same
update it is consitent is only after installing new updates [not all new
ones] this happens)... my guess is there is somehow some interaction
between it and the rest of the kernel where the rest of the kernel
sometimes requires and IP and sometimes not