One more odd thing. When I first added the rain sensor and had issues – I was on firmware version 1.8.2. I thought I would upgrade to the latest before asking for help. I just noticed, however, on version 1.8.3, if I try to add an interval program, the sprinkler basically locks up.
The only solution which seemed to work was to go back to 1.8.2 (which I did) at which time everything worked as expected (with the exception of the rain sensor).
Not sure any of this is related to my rain sensor problem, but thought I would add it as additional information. I am now back on software version 1.8.2