I have five email addresses using IMAP. One of the five will not retain the “Read” status, nor will email stay deleted. All five are from the same provider and are using identical settings in the “Fetching Mail” area. I will mark email as “Read” (either by opening the email or selecting several and toggling the status) and its status will change or I will delete an email and it will vanish. Later I go into the account and everything has been reset. The only way I have been able to mark/delete successfully is to open the web interface and do it through a browser.
This is a screenshot from the “Fetching” settings on the account.
…and the 'Reading" settings