I have never had this problem myself, but searching around the internet it seems to be a common problem.
The main reason for this happening is that, under braking, the Al-ko stabilizer handle fouls the hand brake lever and the handle lifts. The solution seems to be to bend the hand brake lever slightly so that they are no longer in line.
Of course it may be happening for a different reason. But it's worth checking if the handbrake lever and Al-ko handle are in line with each other.
Elnagh Clipper 90.......... Real Names Mike & Hazel