In effect, this usually occurs when when the writers seem to have lost touch with the character and not simply not a simple continuity mistake. To be fair before we go any further, to older shows (i.e. those prior to the year 2000, when they really started to become more serialized), there were situations of the week and the writers focused on plot more than character. The character was changed to fit the plot and not the other way around, so there was very little character consistency in any of these shows.

The writers ruined the characters we know and love. They should just leave the character the way he or she is.

fonzie in fonzie spots anyone see that episode lastone of the series taped anyway