When i submit my form that is being displayed in an overlay, the resultant page is unthemed. If i submit the same form from a regular page view the page is themed as expected. Not sure how to debug this?
Using XDV, Plone 4.2
First off, have you tried to port to plone.app.theming? It should be relatively straightforward (there's a guide in the p.a.theming docs), and p.a.theming ships with Plone 4.2 and is even better in 4.3. I don't think there's a straight-up incompatibility, but there could be. XDV is no longer maintained (as in, it was renamed plone.app.theming and development continues there), so porting is probably going to be necessary sooner or later.
The only other thing I can think of is whether there is some sort of condition or list of unthemed paths kicking in, e.g. may it be looking for a request parameter like ajax_load or the tail end of a path and disabling the theme?
Finally, check whether there are any errors in the console output/logs: XDV doesn't throw a site error, but will log if there's a problem.