Open sub-subfolder in Windows namespace extension

Question

I'm implementing a Basic Folder Object for a namespace extension composed by folders and subfolders (the junction point is a filesystem folder, which is empty). I've implemented IShellFolder, and support returning IContextMenu in ShellFolderImpl::GetUIObjectOf.

Suppose that I have the following folders (where A and A\B are "virtual" folders fabricated by IShellFolder::EnumObjects)

 C:\test.{74660590-4BEF-4BF4-9C85-5FAE0E084926}
 C:\test.{74660590-4BEF-4BF4-9C85-5FAE0E084926}\A
 C:\test.{74660590-4BEF-4BF4-9C85-5FAE0E084926}\A\B

I'm able to open C:\test.{74660590-4BEF-4BF4-9C85-5FAE0E084926}, and it lists the folder A. When I double-click (or select Open from context menu) on folder A, that folder is opened and subfolder B is listed in the view.

Problem: that only works for folders directly under C:\test.{74660590-4BEF-4BF4-9C85-5FAE0E084926}. The context menu is not displayed for subfolder B (and GetUIObjectOf is never called, even though IShellFolder:Initialize is called with the right PIDL).

In the relevant part of IContextMenu::InvokeCommand, I open the subfolder by doing

 SHELLEXECUTEINFO sei = { 0 };
 sei.cbSize = sizeof(sei);
 sei.fMask = SEE_MASK_IDLIST | SEE_MASK_CLASSNAME;
 sei.lpIDList = pidl; // the fully qualified PIDL
 sei.lpClass = TEXT("folder");
 sei.hwnd = pcmi->hwnd;
 sei.nShow = pcmi->nShow;
 sei.lpVerb = cmd.verb.w_str();
 BOOL bRes = ::ShellExecuteEx(&sei);
 DeletePidl(pidl);
 return bRes?S_OK:HR(HRESULT_FROM_WIN32(GetLastError()));