in server/src/jetbrains/buildServer/vsoRooms/notificator/VSONotificator.java [123:129]
public void notifyResponsibleAssigned(@NotNull SBuildType buildType, @NotNull Set<SUser> users) {
final Map<String, Object> root = myMessageBuilder.getBuildTypeResponsibilityAssignedMap(buildType, users);
final ResponsibilityEntry responsibility = (ResponsibilityEntry) root.get("responsibility");
root.put("responsibleUser", getUserDisplayName(responsibility.getResponsibleUser()));
root.put("reporterUser", getUserDisplayName(responsibility.getReporterUser()));
sendNotification(users, root, BUILD_TYPE_RESPONSIBILITY_ASSIGNED);
}