Delete dragged item

Hi there,

As far as I can see, when dragged, a picture can’t be deleted.
I can see that the opacity changes when I drag a box as well so I believe it is on purpose.
Is there a technical reason for this?
Is there a side effect I couldn’t figure out?
Is there a way to work around this?

Thanks for your help and for your very nice plugin.

http://ww.wp.xz.cn/extend/plugins/multi-image-metabox/