ISets of 2 nodes sharing same path from root pretending to be merged

[PARAG00991]

Steps to reproduce the issue:

1. First of all, create a tree by assigning player 1 to all nodes as shown in the figure below:
   
2. Now, if you try to merge isets of the 2 nodes except the root node by clicking firstly on the farthest node from root and then clicking on the node just above it, you'll get the following alert message:
   
3. This was the usual behavior of it. But if we first try to merge the farthest node from root of tree with root of tree first by clicking on the farthest node and then by double clicking on the root node of the tree, it won't do anything but the root node color will become green, after that when you double click the farthest node to select it, it will become green as shown:
   
   
4. Now, if you again repeat the procedure followed in 2nd step, it will show something different.
   It could show the error once, and after that if again you try to merge them it will show something like shown below:
   
   So, these nodes seems to get merged but are not actually merged.