It seems that copying settings for grubfruit and spindly grubfruit works differently for farm tiles. Isn't it the same seed though? And I thought that was fixed at one point but maybe I'm remember it wrong
Screenshot below: 2 grubfruit seeds are available, queueing up planting to farm tile by copy pasting from farm tiles to the right, seems like one seed is reserved for the planting but there is "no pending deliveries" shown on the tile. Reloading the save solves the issue.
Have a farm tile plant with a spindly grubfruit. Have a sweetle tend to it to turn it into grubfruit. Copy settings of that tile to other empty farm tiles. It doesn't queue up planting grubfruit seed as it would be expected