Duplicate alias for different nodes after submitting form twice - Pathauto? I have found this issue, in many different installations of Drupal (I'm running 7.35, but problem occurs even in 7.34 and I think every other previous ones): if I click many times quickly on submit button in node creation forms (be it in administration pages or in forum topic creation pages, I have double-checked it and it occurs in both situations), Drupal creates n nodes with the same content, generating the same alias for different nodes in the same language (content is exactly the same), I checked with this other issue Drupal duplicate alias for same node but no changes, the problem remains. I noticed that even if I don't click so quickly there are many cases in which many of the created nodes have the same URL alias. 

Nodes created with "shared" alias does have "Generate automatic URL alias" unchecked, those nodes which get a different (nnnn-0, nnnn-1 and so on) have this option checked.

Another strange thing is that creation timestamp delta of nodes with the same alias is of exactly of 2ms; I think this generates some kind of problem in pathauto module.
You can use unique_field module to prevent node creation on the basis of field value(unique field).

if this do not help then you can try to use hide_submit module to disable the submit button after first click.