I have a SelectItem which I fill through a Map that has this combo is within a listgridfield, so good up there, but when I select any item in the
If you use a datasource instead of LinkedHashMap, then you can use setValueField method of SelectItem instance. but in this case MAY you can use setValueFormatter method of your SelectItem object.
I had the same/similar problem, my solution that can be seen here ListGrid.setEditorCustomizer in SmartGWT was to use a datasource for the SelectItem and then implemented my own CellFormatter