Several dictionaries' etymologies of English "renegade" trace it to Medieval Latin renegatus, an apostate, one who has denied his religion and gone back to another. Renegatus in turn is the perfect participle of re-nego. But nego is not a deponent verb, so its perfect participle is passive, as in Jesus ter a Petro negatus. But renegatus seems to be meant actively: one who has renounced, not one who has been renounced.
A quick search turned up just a couple medieval writings containing renegatus, and indeed they use it in an active sense. One example:
Quarta fructus [partialitatum] est fidei abnegatio et proditio contra Christum. Conclusio est: quod omnes partiales Christiani sunt renegati et proditores contra Christum, et per consequens proditores Christianorum.
which I take to mean:
The fourth fruit [of factions within the Church] is the denial of faith and treason against Christ. The conclusion is: that all Christian participants in factions are renouncers and traitors against Christ, and consequently betrayers of Christians.
De Impiis Partialitatibus, Bernardino of Siena (1380–1444)
My question is: grammatically, what is happening with renegatus?
Is treating a non-deponent perfect participle in an active sense a normal but perhaps rare grammatical move in Latin (as in English)? If so, what are some other examples? Is it something peculiar to Medieval Latin? Should -atus be understood here as forming not a participle but a related noun, like primatus (primacy) or triumviratus (the office held by a triumvir, or the three men collectively)?
