But isn't the cache rebuilt every-time you start a flight? Or only when starting in a FSDT airport? In this case KIAH was indeed the destination airport
The cache should rebuild automatically ONLY if there was a change in the scenery.cfg, like adding or removing a scenery. If you use a 3rd party utility that disables everything except your start and destination airport, this will force a cache rebuild at each start.
Also, you cannot disable/re-enable an area in flight. Our software only reads the scenery library once, at start. If we wanted to support changes made while flying, we would had to constantly monitor your scenery library, putting an unnecessary strain on the system, while flying.