blown hoses generally do not drop attachments fast. they will drop, but at a controlled rate, as the cylinder still has to expell the fluid in it. i see lines on large excavators blow all the time, and the arm will drop, but not at lightening speeds or anything.
i am pretty **** about lowering all hydraulic attachments to the ground, shutting engine off, and putting the levers in float and bleeding off any remaining pressure. i figure a good hyd system can hold extreme pressure for quite sometime, so by bleeding the pressure off, there is less stress on the system when the tractor is not in use.
alot of modern construction equipment has electronic hyd controls, and cannot be bled off once the engine is shut off.........i still out of habit jiggle the controls after i shut the engine off, even though it does nothing.