As javadocs of the PlayerInteractEvent describe "This event will fire as canceled if the vanilla behavior is to do nothing (e.g interacting with air)", the description does not hold true.

When clicking a side of a block with a flower etc., the event will be fired as uncancelled, thus leading to unwanted behavior.

Video demonstrating the issue https://www.youtube.com/watch?v=565xW9wtpRA

@EventHandler
public void onPlayerInteract(PlayerInteractEvent event) {
    Bukkit.broadcastMessage("Cancelled: " + event.isCancelled());  
}

Minimal reproduction plugin attached.