If you read page 74 of the owners manual, it is all explained.
f button 1 has been pressed to z the right or left, the turn indic-
ators are automatically switched off under the following circum- stances:
Speed below 30 km/h: after 50 m distance covered.
Speed between 30 km/h and 100 km/h: after a speed-de- pendent distance covered or in case of acceleration.
Speed over 100 km/h: after flashing five times.
If button 1 is pressed to the right or left slightly longer, the turn
Indicators only switch off automat- ically once the speed-dependent distance covered is reached.
I can find this in the handbook for the 1250, but not for the 1200.

) but what is a 'speed dependent distance'?