Assigning UTI to file type

I'm trying to add UTI for a pair of file types, matching by extension. I think I've got it setup properly - at the very least, the file extension -> UTI mapping is recognized (I declared it as an imported type in info.plist). However, when I try to get the UTI off of my test file, I get back a dynamic UTI. Here's the sample code I'm using to test these two cases:

NSString *previewTypeUTI = nil;
NSURL *previewFileURL = [NSURL fileURLWithPath:@"/Users/eblair/Desktop/EWF/thetestfile.myext1"];

[previewFileURL getResourceValue:&previewTypeUTI forKey:NSURLTypeIdentifierKey error:nil];
NSLog(@"%@", previewTypeUTI);    // #1
NSString *testUTI = (NSString *)UTTypeCreatePreferredIdentifierForTag(kUTTagClassFilenameExtension, (CFStringRef)[previewFileURL pathExtension], NULL);
NSLog(@"%@", testUTI);           // #2
[testUTI release];

NSLog #1 prints out "dyn.########" and NSLog #2 prints out "com.mycompany.filetype1". I would've expected them to print the same thing. Is there some extra step to get the file->UTI mapping working or is it a case of Launch Services needing to catch up?

Just using the extension->UTI mapping isn't an option because I want to use some APIs that take advantage of UTIs and those APIs seem to be using the file->UTI mapping.

For the sake of completeness, here's the plist entry for the imported types:

<key>UTImportedTypeDeclarations</key>
<array>
    <dict>
        <key>UTTypeConformsTo</key>
        <array>
            <string>public.disk-image</string>
        </array>
        <key>UTTypeDescription</key>
        <string>File Type 1</string>
        <key>UTTypeIdentifier</key>
        <string>com.mycompany.filetype1</string>
        <key>UTTypeTagSpecification</key>
        <dict>
            <key>public.filename-extension</key>
            <array>
                <string>myext1</string>
            </array>
        </dict>
    </dict>
    <dict>
        <key>UTTypeConformsTo</key>
        <array>
            <string>public.disk-image</string>
        </array>
        <key>UTTypeDescription</key>
        <string>File Type 2</string>
        <key>UTTypeIdentifier</key>
        <string>com.mycompany.filetype2</string>
        <key>UTTypeTagSpecification</key>
        <dict>
            <key>public.filename-extension</key>
            <array>
              开发者_如何学编程  <string>myext2</string>
            </array>
        </dict>
    </dict>
</array>

Well, it's been close to a year, but I had to re-address this today and I think I stumbled across what I did wrong. It looks like you need to include public.data as a type you conform to, even though public.disk-image already conforms to public.data. So, the UTTypeConformsTo array should look like this:

    <key>UTTypeConformsTo</key>
    <array>
        <string>public.data</string>
        <string>public.disk-image</string>
    </array>

After making this change, my above comparison of the file->UTI and extension->UTI now yield the same result.