I don't see anyone else answering, so I'll take a stab.
I see that "/userhost <nick>" does add them into the IAL after i've done an /ialclear to remove them from the IAL, however I don't see /protect and /ignore behaving the same way as /userhost does.
/userhost <nick> generates a RAW 302 event, while /protect and /ignore only generate a green info message. It appears to me that the 302 Raw is what's adding their address to the IAL.
I don't know how/why /ignore adds their address mask to the IGNORE list without bothering to take the effort to also add it to the IAL, since it 'knows' it in order to add it.
