Party Poker No-Limit Hold'em Tourney, Big Blind is t30 (8 handed) converter

UTG (t760)
UTG+1 (t1215)
MP1 (t195)
MP2 (t1075)
CO (t1050)
Button (t1340)
SB (t1725)
Hero (t640)

Preflop: Hero is BB with 8[img]/images/graemlins/heart.gif[/img], 6[img]/images/graemlins/heart.gif[/img].
<font color="#666666">4 folds</font>, CO calls t30, Button calls t30, SB completes, Hero checks.

Flop: (t120) J[img]/images/graemlins/club.gif[/img], T[img]/images/graemlins/heart.gif[/img], 2[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(4 players)</font>
SB checks, Hero checks, <font color="#CC3333">CO bets t30</font>, Button folds, SB calls t30, Hero calls t30.

Turn: (t210) 9[img]/images/graemlins/spade.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, Hero checks, CO checks.

River: (t210) K[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(3 players)</font>
SB checks, Hero bets t120, CO raises all-in (t990), SB calls (t990)
-Pot is effectively t1400 to Hero. Hero has t430 behind.-
Hero...

No real reads, however, I feel like the CO plays this a lot like a flush. First there's the (obviously donkish minbet) semi-bluff after two checks. Then there's the check through on the turn and the re-raise of the made flush on the river. Obviously, I'm not holding a very strong flush. If it was the SB who re-raised, I'd consider the idea that he could have a smaller flush than me, since he was playing for half-price. Then, when you consider that the SB calls the all-in, I'm almost certain that someone has a higher flush than I do, but laying this down means that I'm pretty short stacked (not desperate yet, but with fewer chips than I'd like).

Do I/Can I/Should I lay this down here, or is this a mandatory call?

Thanks,
Will