a question about a position in zertz

http://www.boiteajeux.net/jeux/zer/partie.php?id=769

i needed a white marbel to win, so i just place a marbel to sacrifice because i thougt by removing a ring the small group of rings and marbels will be removed and will be mine but instead the game was left with two groups.

the other player win in the next turn.

can someone with more experience and knowlegde of the game can explain what happened? i dont remember this position could happened in the rules.

"You can only capture marbles [by isolating them] if there are no vacant rings in the isolated group. So, you may claim one or more rings when you either put a marble on the last vacant ring of an already isolated group, or remove the ring through which a group of occupied rings gets isolated."

- rules

gracias