SSL_set_client_CA_list(ssl, NULL) problem?

[Claus Assmann]

I'm trying to find what's wrong when I use
SSL_set_client_CA_list(ssl, NULL);
in a server:
openssl s_client still shows "Acceptable client CA names"
(those which are previously set using 
SSL_CTX_load_verify_locations())
instead of the expected
"No client certificate CA names sent"
which happens if I use
SSL_CTX_set_client_CA_list(ctx, NULL)

Now sure what's wrong:
- my program
- openssl s_client
- SSL_set_client_CA_list(ssl, NULL)
- something else

PS: openssl version is 1.0.2t