I thought i lost some XP as well , But thoght it may have just been my tyred eyes playing tricks on me, I thought i saw it go down a little then up a bit while Terraforming, But maybe I was seing things.
Are you using the lines in the co-ordinate bar to judge your relative xp? They move According to what co-ordinates are displayed... A better way to do it would be to screenshot and then line them up with some opacity+colour shifts in photoshop
I'd actually like xp going down on certain actions, with terraforming and cutting trees the obvious candidates, think about it as a method to enhance the preservation of the Lake Tahoe basin.