There are continual references to Dave's dad being disabled and in a wheelchair (comparison to Ironside, better parking space at the wedding, etc.). Yet in the 2008 Christmas episode 'The New Sofa', he is able-bodied with no explanation given as to the change.
When Denise and Cheryl are in the kitchen looking at a clothes catalogue, there is bottle of fizzy orange on the counter, which is seen switching back and fourth with the label intact, then with the label hanging off the bottle.