SSRS Reports unloaded after SharePoint 2013 SP1 upgrade

This gloomy Friday morning I've had a look at the homepage of an Intranet that had SP1 applied last night and I found this on all webparts that had rdl files loaded in them (SSRS reports) and were displaying perfectly fine yesterday.

Not a big deal, if you have the .rdl files in hand :) Just load them again. But has anyone experienced such a problem and have any idea why it happened? I don't.. and unfortunately don't have the time to investigate it properly. The SP1 upgrade went fine with all psconfig steps completing in success.