The problem is that if you define CACHE_DISABLE_ALL the caches get out of sync immediately - this is ok for phpunit, but it breaks install/upgrade - we need a new flag that just disables the read caching and continues to purge/update caches. At the same time we could also implement static caches for upgrades and phpunit to improve performance.

The current hacky workaround is to use cache_helper::purge_all(true); in critical places but it is both slow and often forgotten...