private synchronized Map<Team, StandingRow> calculateStanding() {
          System.out.println("Calculate standing for group " + getName());
          Map<Team, StandingRow> standing = new LinkedHashMap<Team, StandingRow>();

          for (Team team : teams) {
           standing.put(team, new StandingRow(team));
          }

          StandingRow homeTeamRow, awayTeamRow;
          for (Match match : matches.values()) {

           homeTeamRow = standing.get(match.getHomeTeam());
           awayTeamRow = standing.get(match.getAwayTeam());

           System.out.println("Contains key for " + match.getHomeTeam() + ": " + standing.containsKey(match.getHomeTeam()));
           System.out.println("Contains key for " + match.getAwayTeam() + ": " + standing.containsKey(match.getAwayTeam()));
                }
        }

This is my code. matches contains 6 elements, but the problem is that after two matches no keys are anymore found in the standing map.

The output is for example

Contains key for Zuid-Afrika: true
Contains key for Mexico: true
Contains key for Uruguay: true
Contains key for Frankrijk: true
Contains key for Zuid-Afrika: false
Contains key for Uruguay: false
Contains key for Frankrijk: false
Contains key for Mexico: false
Contains key for Mexico: false
Contains key for Uruguay: false
Contains key for Frankrijk: false
Contains key for Zuid-Afrika: false

This is in a threaded environment, but the method is synchronized so I thought that this would not give a problem? I have also a simple unit test for this method and that works well.