PROXY ONLY CONNECT returning error

Hi,

I have a question about Proxy user.

 From DBA account, we defined a proxy user like:

CREATE USER WEBPROXY IDENTIFIED BY mypassword

/

GRANT CREATE SESSION TO WEBPROXY

/

ALTER USER WEBPROXY PROXY ONLY CONNECT

/

alter user isaa grant connect through WEBPROXY

/

At a new connection, if I try:

connect WEBPROXY[isaa]/mypassword

I will receive the error: ora-28058

Only, if I perform the next statement to change the proxy user definition:

ALTER USER WEBPROXY CANCEL PROXY ONLY CONNECT

/

the : connect WEBPROXY[isaa]/mypassword will be success

So in which way it's possible to avoid the connection of the proxy user self (webproxy) ?