While I've had these two modules installed for a while, I think the issue popped up rather recently (although I'm not sure exactly when). I have entityreference prepopulate installed, so that users can click on a link to review different pages on my site. For example, see http://www.gigindie.com/venue/cafe-coda-chico. When a user clicks the "Submit Review" button, they are directed to a node add form for a review, with an entity reference field linking it to the venue. When they aren't yet logged in, they are presented with a login/registration form via the functionality in LoginToboggan.

The url of page that the "Submit Review" link goes to, and on which the login form is displayed is: http://www.gigindie.com/node/add/review?field_review_venue_reference=186

However, after logging in on that form, the user is directed instead to: http://www.gigindie.com/node/add/review

This removes the prepopulate functionality from the url and forces the user to enter information into the reference field instead of it being populated automatically via the url. This is very inconvenient. Oddly enough, if the user clicks the "back" button in their browser from the node/add page that they are directed to, they end up at the prepopulate url that they should have been at originally.

If you need a dummy account to work with to see this on the site, you can create an account, or ask me to post the credentials for one on here. Any help is greatly appreciated, as always.