NSSavePanel setNameFieldStringValue:@"Untitled" bug in sandboxed app

Question

Can't find anything in the doc and it seems to be a bug: if specify @"Untitled" as NSSavePanel's name filed string value, at runtime textfield is empty. If specify anything else – everything works (OSX 10.8, SDK 10.8). And it happens only in sandboxed app.

    NSSavePanel *savePanel = [NSSavePanel savePanel];
//  [savePanel setNameFieldStringValue:@"UntitleD"]; // it works
    [savePanel setNameFieldStringValue:@"Untitled"]; // it doesn't

    [savePanel runModal];

Here is a sample project to reproduce: https://www.dropbox.com/s/catecqe68a0omp3/savepanel.zip

Does anybody has the same problem?