Hi guys.
The lack of answers means that either I wrote too much ( 
) or that this never happened to anyone else. I hope SAP follows up on this issue so this situation can be corrected.
In the meantime, for anyone that has the issue, I though about it and here are two possible workarounds so this doesn't happen.
1st workaround: Replace the second row-repeater with a table (if possible)
I tested it and it doesn't cause any duplication problems in the first row-repeater.
The problem is that the graphic proprierties of a table are a bit more limited than what a row-repeater is capable of.
2nd workaround: Create invisible elements in the second row-repeater
As I said previously, depending on the number of rows in the second row-repeater, the number of duplicated results changes.
I found that, when the number of row in the 2nd row-repeater matches the number of maximum visibile rows in the first row-repeater, it doesn't duplicate any results. (Remember, if max visible rows are 5, it duplicates 5-X rows, being X the number of rows in the 2nd row repeater). If you just make X go to 5, it duplicates 0 rows. So... you can populate your node with multiples of 5, even if some of them are not visible.
So, 1st step: Both row-repeaters must have the same max number of visible rows (lets say Y)
2nd step: Create a visiblity attribute in your node.
3rd step: fill the node with your data.
4th step: if node.size() > 0, calculate the number of missing elements until it becomes a multiple of Y.
5th step: create the elements until it reaches a multiple of Y with WDVisibility.NONE.
Aditional step: everytime your node changes, you're gonna have to delete the invisible rows and perforrm steps 4 and 5 again.
Code example (with visibile rows == 5)
Integer remain = 5 - wdContext.nodeVnMyNode().size() % 5;
remain = remain == 5 ? 0 : remain; // in this case size() is a multiple of 5;
for(int i = 0; i < remain; i++){
IVnMyNodeElement new = wdContext.nodeVnMyNode().createAndAddVnMyNodeElement();
new.setVaVisibility(WDVisibility.NONE);
}
To delete these rows:
for(int i = 0; i<wdContext.nodeVnMyNode).size();i++){
elemento = (IVnMyNodeElement) wdContext.nodeVnMyNode().getElementAt(i);
if(elemento.getVaVisibility()!= null && elemento.getVaVisibility() == WDVisibility.NONE){
wdContext.nodeVnMyNode().removeElementAt(i);
i--;
}
}
I hope this is usefull.