The five past occurrences were caused by a design flaw in the orbiter's
Display Driver Units (DDUs), which also provide power to the orbiter's hand
controllers. The flaw (caused by capacitor discharge) caused the DDUs to
briefly report an erroneous Translational Hand Controller (THC) deflection
when the crew flipped the power switch to the controllers. If the flight
software happened to be polling the hand controllers during that brief
period (it polls once every 320 ms), an uncommanded RCS thruster firing
would result.

I would argue that turning on the THC means that you're going to use the
RCS in the near future, so you shouldn't be in a state where you can't
tolerate a transient RCS firing. What if somebody/something bumps the THC
by accident?

The two remaining failure modes for an uncommanded RCS firing are a
Darlington pair transistor failure in the Reaction Jet Drivers (RJDs), or a
"smart" wire-to-wire short along the lines leading from the RJDs to the
thrusters. The odds you quote are for those two causes.

Those can occur at any time, and seem to me to be the really dangerous
scenarios for a Shuttle-ISS stack.

Jan