If you've edited /opt/bootlocal.sh , your backup file (mydata.tgz) needs to be updated in order for your changes to persist reboots.
If you boot into a desktop session, it will (by default) be done for you automatically if using the "Exit" icon (exittc) in WBar.
Otherwise (i.e. just CLI) you need to run
filetool.sh -b
The kmap boot code is the more convenient way for me, as it doesn't need a backup file to restore this setting from.
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You may want to read this:
http://tinycorelinux.net/book.html