Unstable resaving
Happens because Irrigation is set to buildable but without having an extra cause. Rulesave won't save buildable when it is false. But on load the lack of a value, together with the missing extra buildable cause, casues it to be seen as false.
My understanding is that buildable without a worker extra cause only makes sense in 3.1+ where the player can place an extra. If I'm wrong this should be back-ported to 3.0 too.
A buildable=FALSE appears in granularity.