Three times this year Barclays have put charges on my account when there haven't been any due. Two of these were for overdraft fees when I haven't been overdrawn.
According to Barclays I was overdrawn 5 times last month, attracting a daily fee of 75p each time. Actually I wasn't overdrawn at all, I never am. Because I know I'm never overdrawn the charges catch my attention straight away but I imagine that if I did tend to go overdrawn a few days a month I might not notice if they added a few extra days charges.
I can't imagine that my account's being singled out for a computer glitch so I assume this must be happening to other people as well.