FM 2015: how to fix Charcoal Grey layout zoom/scaling bug on iOS?

I've been working on a branded layout for our Responsive HTML5 output from FrameMaker. I started with the Charcoal Grey layout files, which are available here: RoboHelp screen profiles and layouts‌

I only noticed after customizing the layout stylesheet that the Charcoal Grey layout -- unlike the default and Azure Blue layouts -- has an annoying bug on iOS which causes things to "grow" (not sure what the scaling/zoom issue is here) when the device orientation changes, basically rendering our manuals unusable. Has anyone figured out a way around this? Is there something we can tweak in the Charcoal Grey layout to make it behave nicely on the iPhone and iPad?