Bryan sent this to me but it's useful enough to be public:
Cassius asked about this last night. I did not have a clear answer. According the Plutarch, Epicurus uses a word which centers on the individual who is experiencing pain but he should have used a word that centers on the experience of pain itself (which Plutarch thought was a significant distinction).
Aulus Gellius, Attic Nights, 2.9.1: [Plutarch] declares that [Epicurus] ought not to have said “of everything that pains (ἀλγοῦντος),” but “of everything that is painful (ἀλγεινοῦ)” – for it is the removal of pain (doloris), he explains, that should be indicated, not of that which causes pain (dolentis). Plutarch, in his accusation against Epicurus, is overly meticulous and rather cold, practicing text-hunting (λεξιθηρεῖ) – for these concerns of eloquence in words and phrases Epicurus not only does not seek out (sectatur) but actually attacks (insectatur).
Non inquit ‘παντὸς τοῦ ἀλγοῦντος’ sed ‘παντὸς τοῦ ἀλγεινοῦ’ dicere oportuit – detractio enim significandi est doloris, non, inquit, dolentis. Nimis minute ac prope etiam subfrigide Plutarchus in Epicuro accusando λεξιθηρεῖ – has enim curas vocum verborumque elegantias non modo non sectatur Epicurus, sed etiam insectatur.