The reason for this issue is that, database SEC_CASE_SENSITIVE_LOGON parameter defaults to TRUE in 11G. When this occurs the password sensitivity conversion does not occur. Passwords that are input as lower case are automatically updated as upper case. As a workaround set the parameter to FALSE in the init.ora, run autoconfig on application tiers and bounce the database.
Please refer Note 567116.1 Init.ora Parameter "SEC_CASE_SENSITIVE_LOGON"