Created attachment 196536 [details] html and css showing buggy area in red I have attached a situation where there is a gap injected between lines arbitrarily. This seems to be related to the combination of exclusions/regions/widow/orphans. Where when removing exclusions from one of the earlier elements or removing or changing the values of widows/orphans seems to effect the outcome. The split can be often found in the example region in red. This seems to only occur under specific circumstances and can be tricky to recreate, however it does cause a very obvious issue where there appears to be a random break within content.
This doesn't seem to happen when only the Regions feature is enabled (and Exclusions/Shapes are disabled).
Linking to parent bugs to track
Created attachment 196657 [details] Simplified testcase The bug repros for me on Chrome Canary. It does not require exclusions. The problem combines regions, widows/orphans, and soft hyphens (charset must be utf-8).
Created attachment 196658 [details] Screenshot of bug Screenshot. Notice the linebox pushed into the center region (red) is too short, and the line spacing is off.
Still repros on today's nightly (r151543)
Removing CSS Shapes from the blocker list, since the bug (if it still valid?) is not shapes related.
This bug no longer reproduces for me in the nightlies.