When doing a search in the circulation module for checking out to a patron, one is presented with a list of patrons with names that match your search (if, for example, you only searched on part of the name). Double clicking one of the names should automatically submit the form.
Created attachment 3227 [details] [review] patch
This bug is mentioned in: Bug 5815: Double clicking submits patron selection http://lists.koha-community.org/pipermail/koha-patches/2011-February/013949.html
Pushed, please test and mark resolved