The capturing rules have been changed a few times now quite significantly. Here is how it currently stands:
1) At the end of each turn, the board is scanned for groups with no liberties.
2) The groups that surround it are examined. If any one of the surrounding groups has at least 1 liberty, the surrounded group is NOT captured.
3) If all of the surrounding groups have 0 liberties, then ALL groups will be captured.
Post on the forums if this is not clear.