This is amazing.
as a amateur latin scholar, i believe that rea is accusative case rather than nominative.
I’m pretty sure the accusative form would be ream. Unless it’s not a 2-1-2, but it looks like it is. Also the adjective is supposed to share case with the noun it modifies, so if it were accusative mens would need to be… mentem, I think.
Indeed, mens is nominative: http://en.wiktionary.org/wiki/mens#Declension
And rea is also nominative, which of course it must be to agree with mens: http://en.wiktionary.org/wiki/reus#Inflection