SHAddToRecentDocs doesn't add my file to recent documents - recent-documents

Question

Double clicking on a file in Explorer correctly adds the file to the recent list for my application and I can open it again from the popup menu on my application which I have pinned on the start menu.
I've got a special file manager in the application so I am using SHAddToRecentDocs to add the projects opened in the application to recent files. But it just doesn't happen and I can't find what the problem is.
Here's what I got in the registry:
HKEY_CLASSES_ROOT\.abc\Content Type = application/MyApp
HKEY_CLASSES_ROOT\.abc\(Standard) = MyAppProjectFile
HKEY_CLASSES_ROOT\MyAppProjectFile\shell\open\command\(Standard) = "C:\MyApp\MyApp.exe" %1
HKEY_CLASSES_ROOT\Applications\MyApp.exe\shell\open\command\(Standard) = "C:\MyApp\MyApp.exe" %1
There are no other keys under HKCR\Applications\MyApp.exe.
Like I said, I can open applications by double clicking on them in Explorer, they get added to the recent documents and everything looks fine. I can open them from the popup fine.
My SHAddToRecentDocs call, which gets a correct path, doesn't seem to be doing anything at all. No link appears in the recent documents folder.
Here's the C# code I use to run SHAddToRecentDocs:
[DllImport("Shell32.dll", CharSet = CharSet.Unicode)]
static extern void SHAddToRecentDocs(ShellAddToRecentDocsFlags flags, string file);
[Flags]
public enum ShellAddToRecentDocsFlags
{
Pidl = 0x001,
Path = 0x002,
}
/// <summary>
/// Adds the file to recent files list in windows.
/// </summary>
/// <param name="fullPath"> Name of the file. </param>
public static void AddFileToRecentFilesList(string fullPath)
{
SHAddToRecentDocs(ShellAddToRecentDocsFlags.Path, fullPath);
}

Answer 1

If turned out that a fix to a FxCop code warning was the reason this didn't work.
The ShellAddToRecentDocsFlags API was defined as follows:
[DllImport("Shell32.dll", CharSet = CharSet.Unicode)]
static extern void SHAddToRecentDocs(ShellAddToRecentDocsFlags flags, string file);
Changing it to the following fixed the issue:
[DllImport("Shell32.dll", BestFitMapping = false, ThrowOnUnmappableChar = true)]
static extern void SHAddToRecentDocs(ShellAddToRecentDocsFlags flags, [MarshalAs(UnmanagedType.LPStr)]string file);