Mealwood wont drop seeds when harvested 3rd time from planter box

I would say read the Effects list on the mealwood plant but "Consumes Seed" is not very informative.
Might want to go back to the old line that explains the situation very clearly.
 

As stated. It is correctly functioning Mealwood. It ought not to drop seeds anymore.

For reference see update log.

dig up after 2 harvests or switch to blossom, its early game food which lasts for 60-100 cycles