How I can see all the values in MultiSelect when the focus is in other record?

I had a issue getting the values to stay visible using the multi select field ( PXMultiSelector ) into the location grid. I describe the problem in the text below.

I add a multiselector into a Location Grid in Warehouses in this way:

In the picture before the UOM field is declared in this way:

Aspx

<px:PXGridLevel DataMember="location" DataKeyNames="SiteID,LocationCD">
  <RowTemplate>

        <px:PXMultiSelector runat="server" ValuesSeparator="," AllowCustomItems="True" DataField="UsrFRUOM" AutoRefresh="True" CommitChanges="True" DataSourceID="ds" ID="CstPXSelectorFRUOMId" />

  </RowTemplate>

<Columns>

 <px:PXGridColumn DataField="UsrFRUOM" Width="72" CommitChanges="True" AllowFocus="True" AllowResize="True">

</Columns>

DAC

        #region UsrFRUOM

        [PXUIField(DisplayName = "UOM")]   

        [PXSelector(typeof(INLocation.primaryItemID), ValidateValue = false )]

        public virtual string UsrFRUOM { get; set; }

        public abstract class usrFRUOM : PX.Data.BQL.BqlString.Field<usrFRUOM> { }

        #endregion

This works fine for saving and choosing the values, but the problem is that when you switch to another record in the grid not all the values are displayed.

When you are focus in the field you can see all the values:

But when you are in other record you don’t see the other values.

What property I need to active or what I done wrong?