For many analyses, the Available columns for Input must come from a single table or analysis. When modifying such an analysis by choosing a different table or analysis for input, be aware that previously identified Selected Columns will remain in the input field until you move at least one column from a newly selected input table or analysis into the Selected Columns area.
An exception to this behavior is made for Variable Transformation analyses, where an error is displayed upon selection of a new column in order to protect you from inadvertently losing work.