That sounds like it wasn't actually sleeping all that time. When you pressed the power button, did you actually see the sleep screen before putting it away? And when it was in the pouch where was it? Any chance it might have gone near a magnet that triggered the sleep function?
The latter question comes from some mysterious sleep and wakes that I had for a while with my Glo. I kept picking it up and finding that it would wake up. Or pulling it out of my bag and it was awake. At the time I wasn't using a cover. When I got around to looking at it, I realised that I was putting it down on top of my iPad. And in my bag, I slid it in next to my iPad. The iPad was in a cover with sleep function. What was happening was that I was putting the Glo on the iPad in exactly the right place for the magnet in the iPads cover to trigger the sleep function in the Glo. Mystery solved and I was able to take advantage of this so that I didn't have to manually wake the Glo.
Another thing to do is to restart the Glo. That will restart drivers and the application. If that fixes the power usage, then you can see if it goes bad after a while. If so, there's probably some background process that is having problems and maybe it can be reported to Kobo to fix.
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