activity time instead of load time

I noticed that webpagetest, in some particular error conditions, replaces load time value with activity time;
However, in the detail page, the value is indicated as load time.
In my case this is a problem because I show a chart with Y axis = load time (read by “…/csv.php?test=XXX”,
by click on a single point in the graph will display the webpagetest summary page.
In case of error on the graph, the point (red in case of error) has value = 0 while on the summary page have a value (see image in attach)…
Is there a way to overcome this inconsistency?