dhtmlxTreeGrid drag 'n drop error whet set Colspan

Sorry for my poor English.
I’ve made a treegrid with one column type is tree and set colspan for this grid by the following function:
if (this.getLevel(rId) == 0){
this.setColspan(rId,4,2); // 4 is the index of tree column

And after i drag a parent row and drop on another parent row, their position is unchanged but the content source row (the content of tree column) is copy to the next cell.
When I remove col span setting , everything is ok.I don’t have idea why that error happen.
How can I fix it ?Thank in advance!

Unfortunately it’s not available to keep the colspan after the drag’n’drop. We may only suggest you to call the setColspan() method after dropping the row.