("Note: If auto-commit is disabled (see odbc_autocommit()) and you call odbc_free_result() before committing, all pending transactions are rolled back.")
I've looked thru the code, and that note is definitely wrong, at least in my environment (Windows/SQL Server). odbc_free_result ultimately just calls SQLFreeStmt which has NO EFFECT on outstanding transactions.
In fact, it seems it must be wrong for all environments, because the SQLFreeStmt is bound to the destruction of the result resource. So unset($result) would be just as dangerous - and you're randomly and unpredictably screwed if garbage collection reaps the result set before your transaction's done.