My students and I have noticed a bug that occurs on graphs when you first plot a numerical attribute and then select the axis label and choose “Treat as Categorical.”
To reproduce: Plot a numerical variable on the x-axis to create a dot plot. Then click the attribute name (x-axis), and select “Treat as Categorical.” The dots slide off to the right hand side and out of view. Changing the attribute back to “Treat as Numeric” does not reset the graph to its original form.
A workaround is to change the Attribute Properties (from the table view) to actually make it a categorical variable. Doing so and then dragging the attribute to the x-axis of a new graph produces the expected result (a variant of a bar graph, rather than a dot plot with a number line axis).