Thanks for highlighting this. I believe this is a known issue, as is the issue where the password in Admin -> Email Settings is reset each time the user saves.
Here is a patch fix for this problem. The file to change is /modules/Users/Save.php near line 415.
Before
if($userOverrideOE != null)
{
//User is alloweed to clear username and pass so no need to check for blanks.
$userOverrideOE->mail_smtpuser = $_REQUEST['mail_smtpuser'];
$userOverrideOE->mail_smtppass = $_REQUEST['mail_smtppass'];
$userOverrideOE->save();
}
After
if($userOverrideOE != null)
{
//User is allowed to clear username and pass so no need to check for blanks.
// Fair enough, but the current user interface does not support "change password" like the outbound email settings page so...
$userOverrideOE->mail_smtpuser = $_REQUEST['mail_smtpuser'];
//$userOverrideOE->mail_smtppass = $_REQUEST['mail_smtppass'];
// trim password value
$pw = preg_replace('/(^\s+)|(\s+$)/', '', $_REQUEST['mail_smtppass']);
$userOverrideOE->mail_smtppass = $pw ? $pw : null;
$userOverrideOE->save();
}