Qianqian is right, this is a known limitation. The support library actually monitors when layouts are inflated and substitutes the original widget implementations by the support equivalents. However, this only works for standard widgets…
You can still workaround this limitation by inheriting your custom components directly from the support library version. The procedure is described in this post but, beware, the class names have changed !
Now, for example, you would have to extend AppCompatSpinner rather than Spinner (TintSpinner does not exist any more in support library).