Just put the seeds in your inventory and right-click with the building stick in your hand over the crops. profit

To add to this, a similar duplication also happens with Turtle Eggs, Candles and Sea Pickles due to how the wand makes an exact copy of the target blocks' block states.

Done & done - you can find the new release here once it is approved. This fix should cover all crops & the misc blocks mentioned by acorryn. If you encounter any more problematic blocks, feel free to let me know here or open a new issue over at the Staff of Building bug tracker. Thank you both for the reports!

thank you @Draylar