Dear lammps-users,
It seems like fix store/state doesn't update its values when it stores fixes every so many steps but rather adds them to a running total. See the script below for an example, where a compute reduce averages the per-atom kinetic energy periodically stored by a fix store/state. This average kinetic energy is converted to a temperature variable v_my_temp, which always increases rather than stabilizing when thermostatting the system.
In fix_store_state.cpp, I can see that for when which[m]==KEYWORD, the pack functions set rather than add, but when which[m]==COMPUTE or FIX, the values[i][m] array is always added to. I can only find a place where the values array is zeroed in the constructor.
-Ben