Flags is a property that is only used with a few different elements. It is not saved. There are currently 4 different things stored in flags:

1: "Stagnant" - Unknown Use 2: "skip movement for one frame, only implemented for PHOT" 4: used for liquid equalization, to keep track of which particles have been checked 8: allows sponge to move, or photons to be decorated. (for compatibility with older saves)