Wrong RelayState with Auth0 as IDP

I have the same issue as described here:

but the topic has been closed without any comments.

I have a SP and I want to use Auth0 as an IDP. The IDP is required to return the RelayState unmodified to the SP. See http://docs.oasis-open.org:

If the IdP received a RelayState value from the SP, it must return it unmodified to the SP in a hidden form control named RelayState.

Is there a way to configure that?
If not this is a major bug and prevents us from using Auth0.