[dsmid]

I've found out that Kindle Paperwhite 2 often ignores newly copied update files (Update Your Kindle stays gray).
Rebooting usually helps but the problem is, that an update file starting with lowercase 'u' is causing "Update error 4" on boot.
Solution is easy, rename the update file so that it starts with uppercase 'U'. Kindle ignores such update files on boot.
(That's because boot-time installed bundles are distinguished from usual UYK bundles with that lowercase 'u'.)

From now on, I will name my hacks like Update_*.bin .