STR:

1. Open this page. Wait for the description of the product to load in. The share buttons described in step two render before the product description is inserted.
2. Examine the bounds of the share buttons under the div with class "social-share-buttons" (Twitter, Facebook, Pinterest, and email).

Expected: The bounds of the the share buttons (and the "Add to Cart" button) are correct.
Actual: The bounds of these buttons are incorrect. The bounds appear to be as they were before the product description was loaded in.

Based on some sleuthing in the dev tools, I think that this is a Shopify template thing, so I expect this issue might occur in anything that uses Shopify.

Another interesting feature of this issue is that triggering a reflow doesn't fix the problem.

As Morgan noted in the team meeting this morning, it'd be interesting to know if you can still reproduce this with the patch from bug 1837496 reverted.