Un-freeking-believable. This makes all the difference:

PROCEDURE Init

DoDefault()
select StaffName from travel!supers order by staffname into array This.aList

The problem is the Select creates an array like:

.aList[1,1] = 'value1'
.aList[1,2] = 'value2'
etc...

To make it work, you have to redimension the array to single element:

PROCEDURE Init

DoDefault()
select StaffName from travel!supers order by staffname into array This.aList
dimension This.aList(alen(This.aList, 1))

Which makes the array look like:

.aList[1] = 'value1'
.aList[2] = 'value2'
etc...

Then everything works. How maddening.