In casual vacancy due to resignation, appointment is done by BOD as it is a emergency situation and we need auditor asap, latter approval by shareholders is for protective purpose, if share holders find that previous auditor was forced to resign by management then, they can cancel appointment by BOD and appoint there own auditor.
as the approval is for protective purpose only appointment and working of auditor is all fine till the time it not cancelled or unapproved.
if intention of law would have been that shareholders resolution should decide appointment, they would have given right directly to shareholders and they would have said BOD should propose name. as this not the case it is understood that appointment by bod is all fine, and he can start working immediately
I think unless anything wrong observed everyone is good in the eyes of law. Law makers dont make the provisions keeping any suspicion in their mind. An auditor has right to resign at any point of time there could be many reasons for that. Approval from the shareholders is just an speed breaker thing so that if there is anything wrong happening members can take the action accordingly.
Just because of a suspicion audit cant be stopped so new auditor can continue his work. I hope I was able to solve this mystry lil bit. Lets see wht sir say on this 😉