Upgrading from 1.6 to 1.8 issue

I think the problem may be that in the public directory of those apps there are multiple manifest files and the wrong one is being loaded by rails (an older one). This is a related discourse topic where the same apps you mentioned had an issue:

So there might be multiple .sprockets-manifest- files but you only want the one(s) provided by the 1.8 rpm to be in that directory and the others should be deleted.