Probably old news, but I'm just updating my Lumia 620 to Amber/GDR2 after clearing some space on the phone memory. WPCentral has an article on "Other files" issue taking too much space should be fixed by the update and it seems to have worked for me in the sense its reduced "other files" from about 3.7GB to 3.1GB. Might be worth updating if you haven't already and you're low on space.