Yep - I'd noticed this too, a real shame as it was a graphical highlight.  I've tested this using the Lasgun and it no longer leaves a melting hole in objects - this most noticeable example is the large green 'dump bins' you see - now my shots just pass through.

I really do think this feels like an 'optimization' change and is not likely a bug, as I said a real shame - hopefully I'm wrong.