Context Menu Shell Extensions with VB6

I'm writing a shell extension that will display a menu item in the context menu of folders. I'm using VB6. My extension implements the IShellExtInit and IContextMenu interfaces. I've registered the DLL I wrote and everything's fine, the items are correctly displayed.

There is, however, one problem. When I right-click a folder in the Windows Explorer's folder tree, everything is fine. When I right-click a folder in the list view, however, the CPU load climbs to 100%, which would be unacceptable in the final product. Has anyone experienced this before or can explain where that behaviour comes from?