oh! it happened to my Ichigotchi before too!
I think its a glitch, I dont know what the problem is too...
Yeah there's a couple glitches I've noticed with some V4's.
-the 0 pounds thing
-when snacks only make you gain 1 pound instead of 2
-if you notice setting the date on your tama for february, the date goes past the 28th to 29,30,and 31 (when at the very most it only goes up to 29)