This is not a bug. The Shell GUI shown in Explorer (and partially in Common Dialogs) is more or less organized like this:

The IFileDialogEvents logic is the following:

• OnSelectionChange is triggered by the "Folder View" (usually visible as a list of items and folders) and you can use IFileDialog::GetCurrentSelection() when it's triggered.
• OnFolderChange is triggered by the "Tree View" and you can use IFileDialog::GetFolder() when it's triggered.

So, we can't trust GetCurrentSelection() in the OnFolderChange event.