Problem with Field Picker with latest 9.1 nightly

Hello,

I"m evaluating your latest 9.1 nightly from 2/6/14. I'm trying this sample in my local SDK:

http://localhost:8082/isomorphic/system/reference/SmartClient_Explorer.html#dynamicFreezeFS


I expose the field picker with these settings:
useAdvancedFieldPicker:true,
advancedFieldPickerThreshold:2,


Try it now and display the Field Picker. Drag a column from the Visible Fields to the Available Fields list. Then, try to drag it back to Visible Fields and you get this error as a pop-up warning:

clientOnly add operation failed for DataSource isc_DataSource_8: Duplicate key in record {name: "category",
width: 100,
title: "Category",
columnCode: "c4ef352f74e502ef5e7bc98e6f4e493d",
length: 128,
type: "text",
required: true,
foreignKey: "supplyCategory.categoryName",
nillable: true,
validators: Array[2],
canEdit: undef,
align: "left",
masterIndex: 1,
_selection_47: true,
_selection_45: true}