Just wanted to let you know we found a defect in the firmware in regards to this (was introduced with our last firmware release).
Setting the rain sensor to 'enabled' is not getting persisted on the device correctly.
A workaround is to just power cycle the Iro after enabling this setting. Then it will correctly register and work as normal.
We will put a patch out in the next week or so to fully fix this.
Sorry about the confusion.