Exchange tasks don't sync properly

There’s a good chance I was doing something wrong, but I gave up on trying to sync recurring tasks between Exchange and eM. 
For some reason eM randomly selects Due date for the next occurrence of a task instead of selecting the next one.  It also shows an extra occurrence when I apply a Category.  It also adds a non-recurring task from time to time in addition to a recurring task.  I couldn’t find rime or rhythm to its behavior.  It doesn’t have a problem with tasks with one occurrence only.
I tried to create tasks in both eM and Outlook, but was not able to get a consistent result.
Fortunately there’s a way to turn off task sync in eM.