If you unassign a FlagColumn from a Redefine, you can no longer see the FlagColumnValue expression in the list to remove it. Without being able to remove it, you can't delete the referenced column. So if you want to delete a column you have to know that first you have remove the FlagColumnValue expressions on each of the RedefineSets, then remove the FlagColumn check box, then delete the column. It seems like it would be more intuitive if you attempt to delete a column that is referenced in a Redefine/RedefineSet/OccursDepending that it should prompt and say "If you proceed with deleting this then you will also be removing the FlagColumn/FlagColumnValue/OccursDependingOnColumn assignments for this column as well. Are you sure you want to continue?" and then let the user decide if they want to allow Lysine to delete the related FlagColumn, FlagColumnValue and/or OccursDependingOnColumn columns or if they want to stop and review the effects.