Issue with blank screen was fixed in Flat 1.0.5/Elegance 1.3.1.
But some conflict of styles exists, and we have dev versions of Flat and Elegance with additional option "Enhance Components" that allows to disable jQueryMobile styles for form elements (inputs, buttons, etc.). This way fixes most of issues with JomSocial, but we don't release update because of we are going to make it component-dependent, that is to enable it for certain components only (like JomSocial) and use default behavior in other cases. If JomSocial will be released before this work will be done, we will release current snapshot as a temporary solution.