Do not know if it is YO patch 22.214.171.124 or earlier but currently I cannot unflaten tile with building requiring flat tile (even if it just a plan, not finished construction).
Before it was like that:
I could build corner wall on for example flaten 15.0 tile, then I could lower corner tile to for example 14.5 and flaten it. This would unflaten tile with diagonal piece of wall at 15.0 and bend it along the line of wall (no more flat triangle left out, but smooth transition).
Similar to http://i.imgur.com/wwaI72X.jpg
where guy unflaten palisade tiles (4.0) by flatening adjecent tiles (2.5).
Its not perfect but properly used gives excellent results in aestetics dept. Now its not possible.
Please do not take it away.