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I have rockbox 3.13 installed on a Sandisk ClipZipLooks since I tried modifying the cabbiev2 theme I got problems with USB connection in rockbox.When I connect USB with SD card inserted, rockbox shows an image of a USB-cable and then freezes. No devices get mounted on my PC.
The answer to your problem is to turn off Auto Update in Settings -> General -> Database.
Dev build might be worth a try. Just thought, "unstable" means actually not quite usable.
Also I could not find a clear change log...?
Don't know about the theme modifying affecting USB or not.
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