It takes more than an oxygen release to cause doomsday
Where is Titan's methane ?
With the current temperatures, Titan's methane acts like Earth's water. There's no actual coating everywhere, sometimes there is rain of liquid methane.. which would pose a risk.. but the atmosphere has 2.7% methane. There are possibly oceans of liquid methane, as well as stock of methane inside Titan. Wiki describes these possibilities:
"Energy from the Sun should have converted all traces of methane in Titan's atmosphere into more complex hydrocarbons within 50 million years—a short time compared to the age of the Solar System. This suggests that methane must be replenished by a reservoir on or within Titan itself. The ultimate origin of the methane in its atmosphere may be its interior, released via eruptions from cryovolcanoes."
"Following a flyby on July 22, 2006, in which the Cassini spacecraft's radar imaged the northern latitudes (that were then in winter), several large, smooth (and thus dark to radar) patches were seen dotting the surface near the pole. Based on the observations, scientists announced "definitive evidence of lakes filled with methane on Saturn's moon Titan" in January 2007."
See also this savant commit on Quora. Only a small part of Titan's methane wile be exposed to the oxygen you release.. the part that is in the atmosphere.
ad 1. Cryovulcanic explanation
Current CH4 content in Titan's atmosphere is 2.7% and that will not be sufficient to do any immediate harm, when the oxygen is released. There is no surface coated with methane, the methane is released by vulcanism. Of course, the event would be disastrous when the eruption happens too near to a settlement. With all that oxygen around, you'd get baked. But the oxygen will not easily penetrate into a volcano, against its upward pressure. The gas is pushed out and ignited.
When the methane would originate from inside Titan, there is persisting danger when you release oxygen. The amount of methane is huge, when it can escape at will, you can't do oxygen-based terraformation at all, because the oxygen will be consumed immediately.
ad 2. Polar methane-oceans
Suppose all methane we see in Titan's atmosphere originates from Titan's polar oceans. In that case, it would be very stupid to attempt to terraform it early. You'd increase surface temperature on Titan and evaporate all these valuable methane oceans, before you can harvest them. When the machines that inject the oxygen are accidentally turned on, the oxygen could reach the poles ! a spark of lightning will suffice to ignite the oceans.
But don't panic, Titan is big.. suppose these polar regions only house automated mining facilities, the human colonists living near the equator can only enjoy the fireworks (their children will) but they would loose their valuable CH4 resources and their precious oxygen goes up in smoke. It would be the end of the colony, without the methane profits, why stay there..
Releasing the O2 into the atmosphere will cause the methane to be replaced by CO2 and water vapor. As CO2 is less effective as a greenhouse gas compared to methane, expect to loose some of your temperature gain on the long term. Titan will get colder.