The Thermal Smeltery mod adds TE magma crucible recipes to the tinkers smeltery, including a recipe for destabalized redstone which requires a temperature of 2500C to smelt. To achieve this in a TiCon smeltery you have to put blazing pyrotheum in the lava tank. However the high oven can reach temeratures of up to 3000C, yet the redstone still refuses to finish melting.

I don't know if this issue is fixable on this side, or if @Drullkus will need to fix it.

It's probably a problem with TSteelworks, I'll check that after my finals (unless someone else does it before as it's in 3 weeks)

I think base Tinker's Construct adds the redstone melting recipe.

I thought the high oven only melted Iron ingots?

Oh no it accepts anything that can go in the smeltery plus maybe a few other things (depending on third party mods)