Hello,

Just seen in your code in ColumnsCollection (v. 2010.3)

public UltraGridColumn Insert(int index, string key)
    {
      base.ValidateKeyDoesNotExist(key);
      UltraGridColumn column = null;
      if (key == null)
      {
        column = new UltraGridColumn(this.band);
      }
      else
      {
        column = new UltraGridColumn(this.band, key);
      }
      column.SubObjectPropChanged += base.SubObjectPropChangeHandler;
      this.InternalInsert(index, column);
      return column;
    }
    
    internal void InternalInsert(int index, UltraGridColumn column)
    {
      base.InternalInsert(index, column);
      this.BumpColumnsVersion();
      column.SubObjectPropChanged += base.SubObjectPropChangeHandler;
      base.NotifyPropChange(PropertyIds.Add);
      this.AddRemoveColumnFromCalcManager(column, true);
    }

In Insert you have column.SubObjectPropChanged += base.SubObjectPropChangeHandler;
then at the next row you call  InternalInsert which inside does same registration second time.

Regards,
Maxim Golubitsky