-10706+20 = -10746 on my 15CE

[HKG]

Not a problem of segment or mis-typing.

I just tried to clear flag 8 but got an Error 10
As I wrongly believed that should be flag 7, I cleared flag 7 and the "C" annunciator gone.
Then I tried -10706+20 and it gave the correct answer -10686 !!!

As I wondered if the complex mode was the cause, I set flag 7. Of course the "C" did not appear.
After checking with the manual, I knew it should be flag8.
But now it always gives an Error 10 when I set flag 8
I believe something goes wrong with Matrix. I check the Matrix A has a dimension of 47 x 51 !
I tried f -> MATRIX -> 0 but got an Error 10

Now I have the correct result -10686 but no complex mode or Matrix.
Wonder if a reset helps ? ( by the way, could anyone know how to reset it ? )