You are correct, it's the installation of xposed framework that's causing it. I was just testing 5.1.1 on one of my devices and though 5.1.1 is pretty and has some cool features, I find 5.1.1 too laggy and will revert to 4.4.4. So this is mostly fyi in case others have a similar problem.
1. I've used xposed on 4.4.4 for a long time without problems, including several modules and Aquamail.
2. Rooted 5.1.1 without xposed: no problems with Aquamail
3. #2 plus xposed caused the problem I described.
Xposed is still under development for 5.1.1 and the current problem may disappear with further maturity. At least you know if someone else has a problem. I'm going back to kitkat on that test device, so it's no problem for me.