Tree Nodes are disappearing from the tree

Hi,
We are using Smart Gwt-4.0p.
Issue : Some of the Tree Nodes are disappearing from tree after expanding the folders.
Error in Debug Environment :
00:00:56.388 [ERROR] 13:11:10.404:MUP6:WARN:Tree:isc_Tree_0:Adding node to tree with id property set to:3.
A node with this ID is already present in this Tree -
that node will be replaced. Note that this warning may be disabled by setting the reportCollisions attribute to false.

Issue Reproducing steps:
1. I Expanded all the nodes under root node and I created/deleted/edited tree node.
2. Now reloaded the tree as follows,
Tree grouptree = grouptreeGrid.getData();

TreeNode treeNode = grouptree.findById(nodegrpId);
grouptree.reloadChildren(treeNode);
3. Now I expanded the the tree at second level.
4. I observed some of the tree nodes are disappeared from the tree.
Note : This issue is happening only when I expand all the nodes and do some operation on tree.

Additional Information :
We are using Rest Data Source.
grouptreeGrid.setDataSource(GroupOpertionsDS.getIn stance());
grouptreeGrid.setAutoFetchData(true);

Data source Fields:
//Primary key and Foreign Key Relationship :
DataSourceTextField groupIdField = new DataSourceTextField(
fieldNames.getGroupId(), "Group Id");
groupIdField.setPrimaryKey(true);
groupIdField.setRequired(true);
groupIdField.setValueXPath("groupId");


// Create Parent group ID Field
//
DataSourceIntegerField parentIDField = new DataSourceIntegerField(
fieldNames.getParentGroupId(), "Parent Group");
parentIDField.setRequired(true);
parentIDField.setForeignKey(id + "."+fieldNames.getGroupId());

parentIDField.setRootValue(LoginInfo.getParentGrou pId());

Please give us a solution, how to avoid the node Id conflict exception as mentioned below,
00:00:56.388 [ERROR] 13:11:10.404:MUP6:WARN:Tree:isc_Tree_0:Adding node to tree with id property set to:3.
A node with this ID is already present in this Tree -
that node will be replaced. Note that this warning may be disabled by setting the reportCollisions attribute to false.


Thanking you