I recently upgraded one of our Sitecore sites from 8.0 to 8.1 update 3, which mostly went smoothly.
Since the upgrade, in Experience Editor when adding components, the "Add component" buttons aren't appearing below certain renderings. They appear above the renderings.
Inspecting in Chrome dev tools shows they missing buttons are there but positioned at
top: 0px; left: 0px; and as such are behind the ribbon bar.
This wasn't happening before the upgrade, and doesn't affect all renderings -- but there's nothing unusual about the ones it is affecting.
Does anyone have any idea why this might be?