How to manually update STAT_FLTTIME parameter?

Recently I did parameters reset, thus my all STATs were zeroed.
I do want to restore these parameters but I cannot to.
I set STAT_FLTTIME to my previous value in Full Parameters List window; then click [Write], everything look good.

But after board restart (PixRacer) I see that STAT_FLTTIME is zero.

I just checked my STAT_FLTTIME out of curiousity. Mine is 5600 seconds. I definitely flew more that 5600 seconds. That means it got reset somehow. But the Documentation says STAT_FLTTIME is a ReadOnly Parameter. I was under the impression that ReadOnly Parameters are immutable.

This page says the STAT_FLTTIME and couple of others are resettable and not protected(meaning can be tampered with). They will be reset under the following cases.

  • a different vehicle code is written to the board which clears all parameters (i.e. loading a copter firmware onto a board which was running the plane firmware)
  • user performs a parameter reset

You can use MAVProxy to restore the STAT_FLTTIME parameter using this command
param set STAT_FLTTIME <previous_value>

You can refer to MAVProxy documentation for more details