If you attach a lead to a fence while you have a peony in your hand, the peony top can be placed in the air above the lead without the bottom half.
Doing this with the peony in your off-hand places the peony down normally, it only seems to occur when held in the main hand
This is the same issue as MC-158774. If you relog, the floating peony top-half is gone and your inventory contains the peony again.