It was issued as an OEB (Operations Engineering Bulletin) from Airbus in 1998 and the relevant bit stated...
1) If autobrake is to be used at landingBefore landing gear extension
-Appropriate autobrake mode...... Select
Press the autobrake pushbutton firmly for at least 1 second to ensure the autobrake system is properly armed
The investigation into the incident that EMER_CANC mentions showed that "The loss of autobrake and of the normal braking system was due to a disagreement within the BSCU following a quick action of the autobrake mode pushbutton"
I believe the OEB has now been cancelled though!
