Tonker
Well, I've been there when it happened:
Cause 1: sloppy FO, (me) didn't do after landing checks properly
Cause 2: As the load came on APU failed
Cause 3: APU was U/S but crew forgot and just did after landing checks anyway.
It shouldn't happen 'regularly' and after it has happened once it is the duty of both/all crew members to ensure it doesn't happen again.
Please explain what you mean by regularly Tonkar, if it was a multi sector day and you monitored this happening more than once then it is you who has failed.