Failed validation redirects to normal path I'm using the sub-pathauto module. 

I can edit node 1 of type list from the path list/1/edit. However, when validation fails I'm redirected back to node/1/edit (the normal path). 

Is this a known limitation of the module? Something I have to accept?
In your custom module add below code,It check If url not in alias path, redirect it to aliased path.

function mymodule_init() {
    if(module_exists('subpathauto'){
  $alias = subpathauto_lookup_subpath('alias', current_path(), current_path());
  if (!empty($alias) &amp;&amp; $alias != request_path()) {
    drupal_goto($alias, array(), 301);
  }
 }
}