I feel like I saw a thread on this once, but couldn't find it in a search.
Strange phenomenon - when I compose a new email, the top line starts by saying "Send Using [Default]" which is exactly as I'd want. However, as I type in addresses, selecting them from the suggestions from my address book, the "Default" changes. Sometimes it changes to show the actual default email address, but sometimes it changes to show another one of the email addresses I have configured on the device.
it will automatically select the last "From" email address that you used to send to that particular person. So if you sent an email to BOB from account JOE, then your next email will be from JOE instead of your DEFAULT account.
Aha! Yes that would seem to explain it, thanks! Definitely happy I can monitor and change the From address, and I suppose logically it functions as makes most sense. I just guess I wish it didnt!