Just to add a personal experience a very close family member leased a new Ford Escape a couple of years back and had a similar experience (non hybrid model). She was stopped at a red light with her foot on the break and the engine went full throttle. Lucky for her she had her foot on the break but the suv did jump a foot before it came to a stop.
There is really no excuse for not having a mechanical backup to the system and the more companies that will be going the route of consolidating mechanical functions with electronic means we just have to give way to the possibility of errors becomes greater. Now that HUD's are becoming more popular what's to say a bug in the software won't obstruct your entire view of the road in front of you? Maybe a bug in the NAV system will take certain control over the vehicle to prevent a perceived collision where there is none. Technology is meant to assist the user not supersede them. As this technology becomes more prominent it will just bring the focus to the malicious to tamper with it for what ever outcome they choose. We are also putting a lot of trust in something like a battery. Currently if your engine fails you still have control over the vehicle apart from acceleration, on a fly by wire system once it loses power all those components will cease to exist as well. If we look into real possibilities such as corrosion of the contacts that deliver power, short circuits, blown fuses and battery wear/defects these will make a much larger impact on the driver then ever before. Many people even as we speak may be driving around with some fuses blown but now that the power involved is much greater the systems involved in regulating power flow become much more involved and again more likely to cause a complete system failure.