12 WPMU Plugins or More Breaks Upfront Themes

This applies to all upfront themes:

When i activate 12 or more WPMU plugins (inc dashboard) the upfront themes are broken; it is not one singular plugin causing the issue as far as i can tell.
I have tried enabling all of the plugins by themselves separately without issue, and then tried 11 of them in all different combinations but as soon as i enable a 12th one it breaks the theme... Very weird.

Any takers?

Sam J