Ohh, sure, you should have told that before !!
Your original message was misleading, you weren't login in as a new user, as one of the "su" features is precisely to preserve most of the original user environment variables.
You can still use su for the behaviour you expected, but with the dash option.
And do not hesitate to consult the Solaris manual pages before posting, "man su" is clearly explaining how the environment is passed.
