List in forms dialog only has width when called with other items

When calling

    zenity --forms --add-list my_list --list-values="one|two|three"

the resulting list has minimal width making the list unviewable. If called with something else , it assumes the width of the other item, like

    zenity --forms --add-list my_list --list-values="one|two|three" --add-entry "TEST"

 This doesn't happen with any other item called by itself, for instance

     zenity --forms --add-combo "TST" --combo-values "one|two|three"

will assume width sufficient to display all the items