Per the manual, there is a brake which is disengaged when using the switch:
"Once the control switch is released, the brake sets securing the bed(s) in that position."
There is a brake test on page 11 of the manual:
http://happijac.com/images/pdfs/Bed-...Manual2012.pdf
There also appears to be a brake release on the back of the motor, so might be worth looking at that.
I also found a part that is a "brake adjustment screw" - why that isn't referenced in the manual, dunno... I'll be one of our resident techs know though!