I know that scheduled Freesat recordings used to fail to record whilst in non-freesat mode. Is this still the case?

It's no different afaik.

If you go into non-freesat with a freesat recording due within 15 mins the recordings will not start. If it's greater than 15 min away the box will warn you, stop any non-freesat recordimg and switch back to Freesat mode to make the recording

What I've found with the latest firmware is that if I've left the box switched on in non-freesat mode it'll jump to freesat after outputting a warning, stopping any non-freesat recordings in the process.
But, if I've switched the box OFF in non-freesat mode, any scheduled freesat recordings will fail.

(I assume we are talking Humax here?)

Yes, sorry, I should have added in my OP that it was on the Hummy. Annoying to have to check scheduled recordings for anything imminent (within 15 mins), before switching to non-freesat mode.