SLComposeViewController won't dismiss its parent VC

Question

I'm presenting a SLComposeViewController for sending a facebook message. Presenting and posting works fine and the completion block is getting called (all logs are there).

The problem is, when the posting is complete, I also want to dismiss the current view controller (which is presented via a modal segue in storyboard).

I cannot get this VC to dismiss via [self dismissViewControllerAnimated:YES completion:nil]; inside the block.

- (void)postToFacebook
{
    NSLog(@"Posting to Facebook ...");
    if ([SLComposeViewController isAvailableForServiceType:SLServiceTypeFacebook]) {
        NSLog(@"Facebook is available ...");
        SLComposeViewController *fbSheet = [SLComposeViewController
                                               composeViewControllerForServiceType:SLServiceTypeFacebook];
        [fbSheet setCompletionHandler:^(SLComposeViewControllerResult result) {
            // [self endQuiz];
            [self dismissViewControllerAnimated:YES completion:nil];
            NSLog(@"FB post complete");
        }];
        [fbSheet setInitialText:[NSString stringWithFormat:@"I just scored a %i on this game", self.totalPoints]];
        [self presentViewController:fbSheet animated:YES completion:^{
            NSLog(@"Completed showing FB sheet");
        }];
    } else {
        NSLog(@"Facebook not available");
        [self endQuiz];
    }
}

I've tried variations of block-safe selfs, thinking maybe self was referencing the wrong controller in the block. No luck there, either.