Does Game Center score syncing work for sandbox accounts?

Does Game Center score syncing work for sandbox accounts?

I'm developing for iOS 6.0 and submitting scores to Game Center.
Everything works fine when I submit a score with an internet connection.
When I turn off my internet connection and submit a score that should
update the leaderboard, the completion handler is invoked without any
error. When I turn the internet connection back on, I'm expecting GameKit
to forward the score to Game Center and for the leaderboard to be updated.
But it doesn't update, not even after a long while (1+ hour).
The player is authenticated when the score is initially submitted and
again when the internet connection is turned back on.
Am I missing something? Does it work for sandbox accounts? My score
submission code is below:
- (void)submitScore:(int64_t)score category:(NSString*)category {
//1: Check if Game Center features are enabled
if (!_gcEnabled) {
return;
}
//2: Create a GKScore object
GKScore* gkScore = [[GKScore alloc] initWithCategory:category];
//3: Set the score value
gkScore.value = score;
//4: Send the score to Game Center
[gkScore reportScoreWithCompletionHandler:^(NSError* error) {
[self setLastError:error];
BOOL success = (error == nil);
if ([_delegate respondsToSelector:@selector(onScoresSubmitted:)]) {
[_delegate onScoresSubmitted:success];
}
}];
}