The exact scenario with reproduceable steps are still unknown. The issue seems to appear when an administrator uses the "Manage Web Parts" feature in Central Admin to provision the web parts to web applications or site collections. R&D has logged this issue and will follow-up with further investigations to determine the cause and find a solution for this. The ID# of the item is 259290.
Apart from the above mentioned workaround to retract and redeploy the web parts solution package, it is also possible to copy directly the folders containing the JavaScript files from another environment where the web parts are working fine to the wpresources directory.