The spec 9.1.2. Layout Rules defines "ignoring ... any forced line breaks".
1. Open http://test.csswg.org/harness/test/css-writing-modes-3_dev/single/text-combine-upright-break-inside-001a/format/html5/
Test should render the same as "Reference Page" tab.
Note that since the test does not have prefix, you will need to add one, or use bookmarklets <http://kojiishi.github.io/tweak-css-tests/> to reproduce.
chrome bug: http://crbug.com/663308