As you can (hopefully) see from the images above, there is a Briar seed on the far right but I cannot use it in my flower vase because I deconstructed a vase early in the game that was waiting on a delivery. So, it still thinks there are zero seeds in the world, and isn't counting that one.
1) Build a Flower Vase 2) Choose "Briar Seed" and click plant. 3) Deconstruct Flower Vase before seed is planted 4) Build another one 5) Note that it still thinks you used that seed. (For example, if you had two seeds left, told them to plant one, deconstructed before planting, then made another, it will still claim you only have one seed left)