I've been driving round roundabouts on the way home tonight to see if mine did this - they cancel fine, so far...
Generally you'll have a little sticky-out bit on the steering wheel end of the indicator switch. The sticky out bit gets clicked by a lug-thing on the steering column when you straighten the wheel out, in order to cancel the indicator and flick the stalk back to the neutral position.
One thing I noticed in the Leon is that the 'click' that you would normally hear when going onto full lock with the indicator activated is VERY quiet (say, indicating right and turning right), which would make me think that the action of the sticky-out bit versus the action of the lug thing is extremely soft - perhaps too soft.
Either the indicator stalk AND wiper stalk will need to be changed, or just the indicator switch. Sometimes the indicator stalk and wiper stalk come as one unit and sit over the top of the steering column in a horseshoe shape, other times they are seperate little boxes that screw in individually.
I had one go in my old
Ibiza, and it was a 20 minute fix. Annoying nonetheless though!
On a side note, I am glad we don't have the Vauxhall type stalks, which are always in the horizontal position. I once did a 7 mile journey and was indicating left and right the entire way trying to make the things stop flashing
