The new MP code has a problem with inner polygons that touch the outer.

What you say makes me think that whenever the splitter splits an inner polygon it's going to cause trouble because it splits outers/inners along the same line so they will always intersect then.

There is more to it than that, because these hollow buildings in Montpellier http://www.openstreetmap.org/?lat=43.60807&lon=3.89275&zoom=17&layers=B000FT... also provoke the error message. They do not straddle the tile boundary and the inner and outer do not touch. They do, however, appear to be rendered correctly. I say "appear" because this cannot be seen in RoadTrip because it draws buildings and the background in exactly the same colour, and even on my GPSr it is very hard to see because buildings and background come out almost the same.