The new brown: Huge overbets

[twang]

I guess this post is low content.

Early in an MTT and everyone at the table still have about their starting stack, $1000 or so. One caller in EP, two folds, I raise 4xbb with AJs, everyone folds, limper calls.

Flop comes J-high rainbow with no obvious straight draws. Limper makes a tiny bet, I make a raise of about 75% of the pot. Limper re-raises with 3/4 of his stack (which is a strange bet - why not go all in while you're at it?).

Anyway, I usually fold this because TPTK does not feel that
great anymore. However, I've noticed that villain's move is very common, which led me to belive that this bet does not mean a flopped set or some other strong hand. Is this some kind of default action for aggro players that missed the flop (with an already weak hand): Got nothing? Make a weird overbet or go all-in.

Has anyone else noticed this? If so, what do you do with TPTK when facing a huge overbet from an unknown?