> The *Warnings* buffer is there, it's just that the client frame doesn't show it.
Sorry, yes that's what I meant.

> Why should it?

For the same reason that the warnings buffer is displayed in a regular emacs instance if there have been any warnings emitted during startup.

> how should it know you want that particular buffer displayed without any indication from you?

I think the warnings buffer should be displayed in the first emacsclient created after startup (if there are any warnings). Then the following clients shouldn't display the warnings buffer, because the user has already seen it.