It's fairly common for homes that are under contract (pending or active under contract) to remain posted on the MLS and therefore show up on trulia, Zillow, Homes, or Realtor. This is usually the case because there are contingencies that need to be satisfied: financing, inspection, attorney review, HOA, etc.
The fact of the matter is that there are a good number of homes that go "pending" and return to "active" status after a few days because of these contingencies not being worked out. So if there is a property that you have interest in, you can still monitor its status in hopes of it returning to "active."
Hope this information is helpful.