I very, very seldom see this happening under normal use anymore. I wouldn't say never, but almost. The DB can be broken--for example, there have been a few issues with Calibre in the past when something in Kobo changes and the Calibre driver hasn't caught up yet. I've seen it break when people unplug the USB cable without properly unmounting. An example of this would be when numerous books have been added at one fell swoop and they are not done processing.
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