Elijah Hixson discusses an excellent example of the importance of doing textual criticism on church fathers.
Elijah’s particular example is the phrase εἰς γενεὰς καὶ γενεάς in the Tyndale House Greek New Testament and related phrases in Origen and Chrysostom.
But the principle applies much more broadly. As wonderful as it is to have things like Migne’s editions available so easily online, it remains necessary to consult more recent critical editions to ensure you’re working with the best text of whatever father.
For Elijah’s full discussion, see his original post.