"Failsafe" doesn't mean that the part in question is guaranteed never to fail. it only mean that when (or if) it fails, it will fail in the safest condition.
For example: Usually, if an engine anti-ice valve fails, it will fail OPEN - minimal performance loss (unless you fly a 146
) but you still have engine anti-ice.
If a wing or tail anti-ice valve fails, it usually fails in the position selected at the time of failure - i.e. if you need it, you still have it, if you dont' then you don't have to wear the significant (especially in a 146
) performance loss.
Who is to blame? - usually no-one.