The reference test fast/sub-pixel/float-wrap-zoom.html fails on both Mac and Qt with SUBPIXEL_LAYOUT enabled.
The issue appears to be that the left box is 16.5px wide, which in a float gets rounded up to 17px, but in inline layout stays at 16.5px. The following text run is then painted at respectably 16.5 or 17. If the coordinates of a text-run is rounded before being painted, the reference test succedes.
Committed r148664: <http://trac.webkit.org/changeset/148664>
Landed updated expectation. Bug is still valid.
This doesn't appear to happen on bots at this time. Will try unmarking.