When upgrading from 6.x-1.0-beta1 to 6.x-1.0, I noticed that the options for selecting an operator changed from 'OR/NOR' to 'filter to these IDs/exclude these IDs', but also that the previously selected operator in the view was deselected.
When no operator is selected, the view seems to default to 'filter to these IDs', which breaks the view if the previously selected operator was 'NOR'.