I have a tablet with WIFI only and therefore no permanent internet connection. I had several problems with such offline IMAP in these situations. When I wrote eMails without a network connection they got sent when I was online again, but these eMail just disappeared from my account sometimes. Nothing in the sent folder or anywhere else. They were just gone, but got at least delivered. Or also when I stored eMails as draft offline sometimes they just disappeared. But since this last update I did not encounter such problems anymore, so that is good.