I'd rather say it's a feature. Before the seeds "sprouted" immediately there was no feedback as to whether you'd planted any seeds or not, making judgement of progress difficult (did I plant seeds, or did I accidentally give the wrong order? Where did I break off when going for lunch?...). This makes me believe it's intentional, but that the implementation leaves a bit to be desired.
Maybe some overlay to indicate seeds have been spread instead? (Their disappearance could easily be explained with birds eating the visible ones). Or the soil being disturbed?