This seems to sometimes cause a slight vertical jitter when scrolling large math formulas.
These large formulas are properly scrolling side-to-side, but if you try to scroll them vertically they sometimes jump a pixel or two up or down apparently capturing the scroll event so it doesn't bubble up so the page itself can scroll.
You can see the issue in the animation here: http://imgur.com/a/P97nq (the file was too large to attach to the ticket).
The jitter issue goes away completely if the 'mwe-math-fallback-image-inline' 'vertical-align' is disabled.
It just seems odd to be setting a 'vertical-align' in terms of negative 'ex' units (relative to the x-height of the current font). I am not a css wizard, so there may be a great reason to do this which I'm not aware of.
( We could, of course, override this CSS in the iOS app to fix the issue we're seeing, but I thought it better to make a ticket tagging Math and MobileFrontend to see if others have more info. )