ubuntu unity "double click" opens folder not file

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http://askubuntu.com – I've been using 12.04 for some month and have had this issue (I don't know if it's been there all the time or I did something that made it happen): Whenever I double click a reference to a file (say in firefox downloaded files list or a list of files in gnome search utility) rather than opening the file directly the folder where the file resides is opened and the file in question is selected. It happens as far as I can tell on applications that uses xdg to open other files (it also happens when I open files from links in zim-wiki). I realize this may be a feature but when I'm looking for som (HowTos)