To be quite clear about QF32 and similar failures:
In ANY multispool engine, IF the high-pressure spool keeps running after a shaft separation of (one of) the lower-pressure spools, that low-pressure turbine will be driven to an overspeed condition.
Thereupon, one of perhaps three things will occur:
1) The turbine blades will, by design or accident, suffer a blade root failure. This creates medium-energy shrapnel, but also removes the driving torque from the free disc, so it can coast to a stop without further failure. eg QF74, SFO 744, RB211 engines.
2) If 1) doesn't happen, the free disc assembly will be driven aft where the blades will contact static parts such as a downstream nozzle guide vane ring; this will beat up the airfoils to the point that the disc stops accelerating. I have seen CF6 failures of this type.
3) if 2) doesn't happen, then the disc may continue accelerating to the point that it bursts. I give you QF32, Trent 900 - and also perhaps the T1000 test bench failure a few weeks before QF74.
Turbomachinery designers must take shaft failure into account in the design process. Some may do a better job than others.