Call Back key 6 on MX-One

[BlAle]

Have a good day and successful completion of 2018!
An unpleasant thing happened with TSWSP04 / R5A.
Suddenly, CallBack for key 6 stopped working.
The CallBack key works fine, but the "6" key is not.
Does not work on all devices in all LIMs.

Looked ASPAP: PARNUM = 19; PARAL = 6 as it should be.
I guessed to play with the value PARVAL at PARNUM = 19

ASPAP: PARNUM = 19;
APPLICATION SYSTEM PARAMETERS
PARNUM PARVAL
19 6
END

ASPAC: PARNUM = 19, PARVAL = 7;
ASPAC: PARNUM = 19, PARVAL = 7;
SURE? (YES / NO)
Y
EXECUTED

ASPAC: PARNUM = 19, PARVAL = 6;
ASPAC: PARNUM = 19, PARVAL = 6;
SURE? (YES / NO)
Y
EXECUTED

ASPAP: PARNUM = 19;
APPLICATION SYSTEM PARAMETERS
PARNUM PARVAL
19 6
END

That is, changed to 7, then to 6. ASPAP. Again the result is 6.
But now it works!
PARNUM = 19 did not change from installation, more than 10 years. DUSYI do regularly.
This is the first time I have met such a discrepancy with what I saw and the real one in the MX-One.
Some kind of mysticism ..
Has this happened to anyone?
I do not know what to expect next.
There is insurance against such failures?