50 NL have a set but CO takes a strange line

[seki]

Smells like TT/88, but I can't fold here. When you play mid/small pps for set value, you're taking into consideration the fact you pay off in set over set situations. People take strange lines all the time, and the small chance that he's playing oddly with anything other than an overset or turned straight (checked the up and down on the flop? bleh) is enough to call. Almost half your stack is already in the pot! Would you fold with these odds if the action had come on the flop?