Hahaha....in Indonesia it's no problem to call another woman "Ibu", even though she is not your mother.
It's a poilte form to address a woman.
It's used a lot in direct speech, also to avoid the use of the 2nd person singular.
(here are some examples):
That's interesting. I know a number of languages in which referring to a woman older than oneself as "mother" or "auntie" is common, but I always think of it as colloquial or familiar, the sort of thing one might say to somebody who runs a shop, but not one's teacher. I looked up its use, and it looks to me like "ibu" (or "Bu"?) is a standard formal way to address a woman, right?