DataValidation of a list with defined names is not taking the source into account. As a result, values are not displayed as options in the cell drop-down list.
If the Spreadsheet ribbon has a custom template which hides the Style Gallery, when the Styles collection is edited, a NullReferenceException is thrown. This is because the change causes changes in the Style Gallery while the template of the Style Gallery is not yet applied.
Having more than one rule over a cell range and managing the rules through the "Manage Rules" dialog so they switch priority does nothing and the cells do not update.