I was using junk seeds to plant grass this morning. I wound up with one stack of 4 seeds and another of 1 seed. All were the same crop. (Green kale, as it happens.)
Planting grass failed, claiming I didn't have seeds.
When I combined the two stacks, I was able to plant one more grass tile.
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As "bugs" go, this hardly qualifies. It's a nit with an obvious workaround. But I figured I'd report it anyway, in case it's easy to fix.
Even better would be if it could combine seeds of two different crops.