How are you rebooting your system? Because if you created a button/script that runs the command "shutdown -r now", your desktop environment won't be able to save the current opened windows and will revert to the last saved session. The proper way to reboot/shutdown is to logout kde first and then issuing reboot or poweroff at the command prompt.
BUT, if you have that script/button and want to keep it, go to BT Menu > Settings > KDE components > Session Manager and under "On Login" select "Start with an empty session".
Yes, erase all the other keyboard layouts on the configuration page, your layout will be always default.




