Launchpad prone to spontaneous combustion

[DaMachinator]

Launchpads are made of a material that is highly flammable when subjected to high loads. Suspected mods: KJR and (possibly) SpaceY.

Steps to reproduce:

Find something big to put into Minmus orbit. Preferably weighing 200 kilotons or more.

Add large-diameter SpaceY parts and other things until it can get to Minmus orbit, in the same manner as you would build a regular craft. It should weigh somewhere around 1 megaton or more.

Add the big SpaceY launch clamps. (And probably the stock ones too, for good measure.)

Set up the staging such that the first stage activates enough engines to go up, and the second stage disengages the launch clamps.

Launch the craft.

At either main engines start or launch clamp release, the launchpad should spontaneously combust without injury to the rocket.

This happens fairly dependably with anything bigger than 1 megaton that use launch clamps. Unfortunately, I have been unable to determine whether this is ALL launch clamps or just the big SpaceY ones, as it does not happen under a certain craft weight (or maybe thrust) and the stock launch clamps look woefully inadequate for anything of this size. I should probably test this again with a LOT of stock launch clamps instead of 4-12 big ones.
 

While I know that I'm on an unsupported version, I am looking for tips on how to narrow this down to a more specific set of actions. In addition, I have no idea whether this issue persists in the latest version.

Edited July 29, 2016 by DaMachinator
I cans spell so gud!