Shadowcatcher by itself works fine but if there is an object that needs to be Mate as well then it is not good.
As soon as there is Add Holdout Shadows to Beauty turned on it adds shadows to Mate object as well.
For exmaple in this case:

- there is grid added to shadow catcher node
- sphere and rubber toy are in rendergemoterysettings and turned on Matte holdout
- Craig is fully there.

We can see shadows on both Sphere and Rubber toy as well as on grid. Instead we should see all shadows on grid as they are but sphere and rubber toy should be Matte completely including shadows.

This is a side effect of the fact that the shadow catcher itself is a holdout - karma can't distinguish shadow on background/shadow catcher holdouts vs matte holdouts which leads to this problem. Can you please file a bug? In the meanwhile the only workaround I can think of is to render shadow catcher in a separate pass (with shadow casting objects as phantoms).