41CL MMU Backup

[twoweims]

What is the proper way to backup and restore the MMU Configuration (Page 804)
to / from Flash Memory.

If I write YFWR page 804 to page 3F1 I can see that the CRC of page 3F1 is getting changed. The 41CL Manual seems to be silent on the procedure for restoring page 804. I tried MMUDIS, MMUCLR, then YMCPY with 3F1>804 in ALPHA. When I enable MMU the calculator locks up with a constant tone until I remove the batteries.

I am obviously missing some important step.
I would appreciate any advice on this and also to learn some backup strategies/best practices from fellow CL users.