OK, I have tested one of my own WD7 sites and can see what you mean when exported by MX, I can also confirm that disabling the viewport metatag by add following name to any object in the document: NoViewportMeta works perfectly by returning to the viewport zoom level you were used too before Xara added this meta.

I'll find out what's going on, however I do know that the viewport meta was added to fix display issues with iOS.

Stay tuned