This happened to me this past Wednesday at an Amatuer Poker Legue game.
I am on the button, we are in the third hand of the game so everyone pretty much has t3350.
Action starts:
Button - Wooderson:
SB
BB - Villain
UTG1
UTG2
MP
CO
Ok, pre-flop pretty much all stay in as it comes to me, I raise t260 to make the total bet t300. BB, UTG1, MP, CO call. All others fold.
Flop comes:

. I have top pair and iffy 3-to-a-flush. BB bets t100, UTG1 calls, folds to me and I raise t300 to t400. Both call. Pot is now t2700.
4th street:
BB bets t200, UTG calls. I raise t400 to t600. Both call. At this point I am astounded. I have TPTK against the BB. She is an older lady, let's say about 75, who won the prior hand with a full house she wasn't aware she had. I put her at best on trips. Pot is now t4100
River:
I have my flush and fourth to the nuts. I don't think BB had quads, and based on the fact that she just had a full house and didn't know it I don't put much stock in her play. She has limped constantly in all three hands we've played, so I also don't think she's got any full house that's out there.
She bets t200 again. Here is where I make el grande mistakeo - I raise t1850 to make is t2050 and I cover her by about t100. Why raise? I think I have the best hand, just take it down... I don't know. She calls and I flip my AK.
"I knew you had the flush but I had trips and had to call." She turns over wired-8s revealing she has a full house. But she gets up to leave the table and says, "Good luck all."
Everyone reals her back in - second time she wins and has no idea. Holy poop.
She's either daft, or bluffing her entire persona.