When you double-tap on a paragraph on mobile the zoom changes to match the width of the paragraph.
After the site upgrade, when you double tap a comment on a question or answer, the zoom level remains unchanged.
Browser is chrome on nexus 4, if relevant.
Update
This question explains how to disable it: How to disable double tap zoom feature in Chrome 30 on Android (Nexus 10)
Probably the mobile version has a viewport set