Created attachment 219456 [details]
Atm, I can only repro this after implementing the fix for Bug 125829. I'll update this report with a test case that repro by simply turning subpixel on. (not requiring other changes)
This and Bug 125829 are more like placeholders to discuss the rounding strategy (if needed at all)
Same situation as bug 125757.
Created attachment 219801 [details]
observed on bugs.webkit.org
Created attachment 219802 [details]