His his series he could place down multiple mines, so by him only being able to place 1 was already a nerf. As much as I hate this move spammed by Isaac's it doesn't exactly need a nerf. If any of it's properties were changed then it wouldn't be able to combo into. Without defense it would be way to easy to destroy like Jak's "yellow drone." Yeah overall it doesn't need anymore nerfs.
My own personal theme song! http://www.youtube.com/watch?v=fL0nWoHG11Y