Problem With Number of Players Advancing

I am the TD in a tournament (the 5 x 5 (III)) which I set up for 25 players in 5 player groups, no tie-breaks and at least 2 to advance at each round.  More than 2 could advance because of the no tie-breaking situation.  Because of the no tie-break feature, there is a round 4 although there would have only been 3 rounds if tie breaking were used (25 in 5 groups; 10 in 2 groups; and 1 five player group).  

Round 3 was made of up 2, 3-player groups, but only 1 player advanced from each of the groups.  One of the players was counting on two players advancing from each group in round 3, and made strategic decisions accordingly.  Because of this he did not win his group and did not advance even though he was second in the group.

I need to provide an explanation to the player, and would like some help with this.  I assume that it's a feature of the no tie-break feature and maybe some limitation about more than 50% of the players in a group advancing.  Am on close? 

The tie break being used or not is not relevant. As previously stated the limit is 50% plus ties.

http://www.chess.com/tournament/50-1 is a 5(2)->2 format tournament.

http://www.chess.com/tournaments/pairings.html?id=21774&round=4

Group #1 - Two of two players advance due to a tie.

Group #2 - No ties so one of three advance due to maximum 50% limit.

Thank you for the explanations which have been most helpful.

Just remembered there is a little wrinkle. If there were seven players so there were groups of three and four, the programming would have calculated 50% of four is two. Two would be advanced in both groups.

You can see two of three advance here in Group #1  http://www.chess.com/tournaments/pairings.html?id=10034&round=2

I had always thought that this applied only to the initial configuration of the tournament's settings. That is, if five players are in a group, the TD could not specify that three should advance. But I had figured that if two are specified to advance from the beginning, then that always applied to each round, regardless of group size in the subsequent rounds.

How disappointing.

Oh man, I am bummed.  I made it into the pentultimate round of a tournament with 100 players.  I just won my last game in the pairing, cementing my second place.  I was thrilled that I would be advancing to the final round.  But only the top player in my group of three advances. :(

We clarified several months ago that the number of people advancing from one round to the next must be no more than half the size of the group, except in the case of ties not broken by the tiebreak score, regardless of the parameters specified at the outset.

However, in this tournament, the size of one of the groups is three. One was banned for cheating, and both of the remaining participants are advancing. How can this be possible?

http://www.chess.com/tournaments/pairings?id=40283&round=3