Hi hikoushi, am just off to work, but for a quick answer talk to Honeywell or whoever made your aircraft's FMGCs.
It sounds like a fault, caused by a bad connection which was cured by re-racking the FMGC's. I was not talking about fault scenarios, but a similar thing would have happened to a Boeing with a faulty FMGS, so it's nothing to do with Airbus per se, or Airbus being "overcomputerised", which was one of my points.
Not all faults are monitored by ECAM, but you know that right? - and you also know which faults and systems are not monitored don't you?
We always actively run plotting charts when crossing oceans and plot our position regularly to guard against the sort of navigation problem that you mention.
I do not know everything, but from my own personal experience; TRE's do not know everything either.
