Yesterday i wondered what's with the lake Balaton. The coastline is made up from 3 ways which once was one, and the rendering is broken. I could simply join the segments and hope for the best, but instead i went to #osm to ask. As it turned out a change in May broke the rendering, the dev's are aware of this and eventually it will be fixed. So, large objects are a "bad thing" (tm), please do not rejoin them.