Bleach......... Some Isshin questions?

the whole things pretty unclear about isshin tbh. the only soul reaper who has shown any knowledge of him is urahara and god knows that guy likes his secrets. he's been shown out of his gigai a few times (while fighting) but normally remains in it, maybe its to hide his presence from other shinigami, since he lives in the human world he was probably kicked out for some reason like the vizard. he's clearly captain level so its odd that other shinigami never react to ichigo's last name. hopefully all this will be cleared up in the current arc of the manga, his "true identity" was brought into question at the start of it so they might just answer all our questions about him