When I invade a planet with a spore ship or as a "Neutral" ethical civilization, I often knock out all improvement tiles that have a queued task on them.
I only ever invade with Traditional warfare or Information warfare, and I never get a message saying that planetary improvements were destroyed.
Tiles are only wiped out to the level my enemy had researched in tile enhancement. i.e. If my enemy had soil enhancement only researched, after invasion a planet would be filled with orange and red squares, but the yellow ones were all gone.
Orbital terraformers and neutral allignment do not help with this bug. In this case, all the remaining tiles are green, but tiles that corresponded to tile upgrades the opponent would have had just disappear.
Thanks. Just trying to help. Great expansion overall.
