Created attachment 362977 [details] reduced test case See attached test case. Without the opacity property, the emoji is drawn normally. The bug can be reproduced in the latest build (r242083).
<rdar://problem/48405765>
Transparency layer is not big enough. Is this about not getting the right glyph bounds?
Yeah I think this bug is the same as https://bugs.webkit.org/show_bug.cgi?id=6274
*** This bug has been marked as a duplicate of bug 6274 ***