Created attachment 271653 [details] failed test page In the test case, if the F div and the close div tag(</div>) has only one newline, will generate a little gap and cause the align error. But if their has space with the newline, this error will not display. The .box text-align set right or justify will cause this error.
Created attachment 271654 [details] this test will not cause error
Works fine with FF(44.0.2). Fails with Chrome (Version 48.0.2564.116 (64-bit))
Created attachment 271771 [details] Test reduction
Safari, Chrome, and Firefox all agree on rendering for this test case. I don't believe there is any remaining compatibility issue.
This is an IFC progression (legacy line layout still produces gap).