The latest version of the fragmentation spec states that parallel flows (e.g. a float and non-float content around it) should be fragmented independently[1]. Currently WebKit doesn't do that and instead is quite unpredictable when it comes to forced breaks around floats. Most likely multiple patches will be needed to properly fix this. Logging is as a possible meta-bug [1] http://dev.w3.org/csswg/css-break/#parallel-flows
CSS Regions were removed in Bug 174978.