Excellent work, again!

The melted bars thing really baffles me. Presumably that was an actual on-set explosion and not a special effect added in post-production, right? So why did somebody take it upon themselves to think it was not good enough? Is this a case of "Reality Is Unrealistic"? (as they say on TVTropes) Somebody thought what was actually photographed didn't measure up to their conception of what it ought to look like, even though that's what it actually did look like? And for just a couple of frames nobody would notice on their own? What the heck is that about?