As of today (I believe), when entering text (ie asking a question, entering an answer, writing a comment) in mobile safari using the mobile theme, the site zooms in so that the entry area is wider than the screen. This is incredibly annoying, please make it stop.
There's no clean, universal, way to achieve selective zoom disabling.
So we're stuck choosing between hurting accessibility, or having the few people the zooming annoys (it zooms to the content area so... it's not really generally harmful IMO) zoom-out manually.
We're going to error on the side of accessibility until there's a better workaround in all mobile browsers.