Two required y, responses for variability chart

[#1]

Hi,
I would like to create a variability chart, but only with one column assigned to y, response. Sometimes that does work, sometimes JMP requires two columns to be assigned to y, response.
Below two screen shots that illustrate the situation. Can anyone help why that happens and how to solve it?

[#2]

When the Chart Type is Variability only 1 Y column is required, but when the Chart Type is Attribute, it requires 2 y columns.