For the disappearance of multi hex building I belive it is safe to say it is directly the result of the underlying terrain of a multi hex buildings registration hex (normally the top left ) being temporarily turned into rough terrain but it can be a gold plated B!TCH to get it to convert one sometimes with this as proof
I hammered that over and over and could not get the building to disappear
BUT... I could not find a hex showing "rough" anywhere and the test was to see if rough could be created anywhere BUT under a multi registration hex