The commit 7e87eb1 removes the _format param being passed to twig.controller.exception:showAction. No updates were made to the TwigBundle's ExceptionController to account for this change and as such errors or exceptions from non-html requests render incorrectly with the html templates.

One possible fix for this is to update the ExceptionController to rely on $request->getRequestFormat() instead of the $_format argument being passed around in the ExceptionController to its various methods.