Whilst playing minesweeper on this website, I ended up with the following position:
In this, how is possible to solve the puzzle without guessing? Given that there are 4 squares remaining, and 2 mines remaining, it seems to me that the first mine can be located anywhere on the 2x2 squares left and the second mine will be on either of the two squares of the horizontally opposite rectangle that remains unclicked/unflagged.