FindObjects() -> The search with square brackets does not work

The search with square brackets does not work, why? See Pictures...

Sub Test()
Dim oSelection As ObjectItem
Dim oObjects As ObjectItems

Set oSelection = Application.Selection.Item(1)

Set oObjects = oSelection.FindObjects(aucObjUnspecified, aucSearchHierarchical, aucTypeUnspecified, aucAttrComment, aucCondEqual, "Test [Z]"

MsgBox oObjects.Count

End Sub