Yeah for some reason if I turn mine off in ID Scan mode it doesn't start back up in that mode.
I've seen my 780 do that same thing. It is currently turning back on in the mode it was in when I powered it off.
I don't recall what I did to fix it either.
If you have software for it, you might try reading and storing the memory contents and then doing a factory reset to defaults and then load your banks back in a bank at a time from the backup you made.
Double check the radio wide configurations also.
Mine has started an odd thing where the channels will not remain on "Auto" for the step size.
Sometimes it will but then a few days later I may go in and change a frequency that had the step at auto only to find that it rounds my frequency entry to something other than I really wanted because the Step size had changed to a fixed value.
I've yet to figure that one out.
I'm wondering if something with the ram in these old radios is failing as we all know ram does have limits on the amount of writes a cell can take before things start failing. Just like SSD drives.
I would have thought that issue would have been corrected in today's world but maybe not.
I still have some old Pro-2001 scanners and the ram failed in all of them.
I was lucky and found a guy on ebay that had some of the ram chips. I replaced them and both radios hold their program again.
I hope this is not the case with the 780's as they are nice scanners.
That was a concern with the 996T (pre XT) models also. They wanted to do some type of P25 auto adjust but it would have created tons of ram writes which would have caused an early death of the ram in those models. There is a thread here somewhere where UPman talks about that.