No way to do it automatically from non-root user.
Maybe have to place fix to udev rules?
But this is not normal
Seems there is conflict between Linux USB+vfat subsystem VS buggy Kindle firmware.
When Calibre is syncing books, Kindle just turn off USB mode, load main Home screen and disappear from Linux (but Linux show it is still mounted).
I'm sure if Linux kernel developers refuse to fix it for Kindle, must be another way from Calibre side to fix the problem.
Kovidgoyal, if you need any help and/or research for the problem, I can do it.