From the Wikipedia page on it, it seems so. The problem is described as:

  You are shown a set of four cards placed on a table,
  each of which has a number on one side and a colored
  patch on the other side. The visible faces of the cards
  show 3, 8, red and brown. Which card(s) must you turn
  over in order to test the truth of the proposition that
  if a card shows an even number on one face, then its
  opposite face is red?

Perhaps it's a consequence of being a programmer/mathematician and doing this for so long, but it seemed clear to me.

I would have turned the 5 card too. Why? Because it says to test the truth of the proposition. So it's saying all bets are off, whatever I told you may or may not be true. Only what you see (the table with the 4 cards) is real.

If you still assume that each of which has a number on one side and a colored patch on the other side holds, then no need to check 5. But if you focus on testing the final proposition, I'm not sure anymore of what I should assume...

Summary: poorly worded problem.

The proposition:

  Which card(s) must you turn over in order to test the
  truth of the proposition that if a card shows an even
  number on one face, then its opposite face is red?

The rest is given information, not the proposition.