Can torches cause fire?

I was just about to dig myself a new basement to my wooden-home, when I suddenly figured that the ceiling was on fire (long story short, not even the cockroaches survived). The only thing I did was to place a torch underneath a wooden block, as I've done many times before without so devastating effects.

So I wonder, can torches ignite fires? If yes, always or only under certain conditions?

Torches can't cause a fire.

• Are there burned trees in the neighbourhood? A forest fire might be the cause.
• Did you hear a loud "flinging" sound? You could've been unlucky enough to have a ghast around.

According to Minepedia:

Fire is a block that was first seen in Indev. It has an animated face on all four sides, and two faces on the inside at slants. Fire is not created naturally in a map, with the exception being in The Nether, it will only be created if the player or a Ghast causes it or Lava burns a flammable object.

At no point does the minepedia describe a torch causing a fire, suggesting that no one else has seen this happen.

Could it be that your roof is near to a lava flow? Or, you've accidentally used a flint and steel on the wood?

No, torches cannot start a fire. Period.

Lava can ignite things up to 2m away (see the Lava page on the wiki), which would be 2 blocks away... so even if you have the following (side view):

.=....   ( KEY:   = wood  )
......   (        . air   )
~~~~#=   (        ~ lava  )
         (        # stone )

Both sections of wood (above, and on the other side of the stone) could possibly catch fire.

I haven't personally tested this, and will edit with more details once I get a chance to test it, but this could be your problem.