How can the data in the multi-selection (Lookup) field be sorted uppon the original sequence I selected?

How can the data in the multi-selection (Lookup) field be sorted uppon the original sequence I selected?

Hi,
In a form I create a lookup field with multi-selection from another form. It works. But when I picked up my choices and saved and reopened it, the sequence of my choices is changed and by random. I contaced support, he says it's order by the ID(created sequence) of the form which is referred. But I checked and it's not true. Any idea about this? Random order is really a mess to user.