Channel list edits don't persist

Custom FW 4.1.3

I occasionally edit the Channel List, after new channels have been added automatically. Recently I have found that the box seems to have done a full retune overnight, since all the channels numbered 700 - 999 seem to be shown. My channels stop at 301, apart from 704.

I have edited using the box, then imported from the box to the customised firmware. At some later point, and I can't be sure yet whether it's every time I switch the box on, the edited-out channels reappear.

I have edited using the CFW, which is painfully slow since the "Hidden/Visible" cells have to be altered from "Default" to "Hidden" one at a time, and there are lots to be changed. Again, the changes are effected, but do not persist.

What am I doing that's wrong?
More on this: just switched on the box and it showed the channel range 900 - 999. I deleted them, imported from the box to the Raydon database. Exited the browser, then reloaded it to look at the 7 day Channel list. Still shows the deleted channels, but the box doesn't.