Question about splicing since the gardening patch

I thought this was a glitch. I guess it's not! I don't splice plants very often, but I've never gotten a rare harvestable from it. The collectible information/notepad implies that you'll get a rare fruit/vegetable/flower just about every time. Changing that text to make it clear a rare harvestable isn't guaranteed (or at least that it's unlikely) would be really helpful.