The bug
The copper bulbs in the trial chamber are of various oxidisation levels. However only the default copper bulb is waxed, the others are all unwaxed.
This is caused by the processor list trial_chambers_copper_bulb_degradation replacing the waxed_copper_bulb with unwaxed exposed_copper_bulb, etc.
How to reproduce
Find a trial chamber
Inspect the copper bulbs and notice some are waxed and some are unwaxed.
Linked issues
Comments 2
At first glance it may seem intentional, but then I gave it more of a thought.
If the copper bulb's aren't waxed then by the time the player discover the trial chamber naturally (e.g. through spelunking and mining) it's very possible all of them will have grown dim from oxidation, this begs the question: why generate the structure with copper bulbs of different stages of oxidation if the player are less likely to find the chambers in that state to begin with?
Part of the atmosphere and challenge of the trial chambers are to brighten dimmed bulbs, but having the trial chambers generate with all the copper bulbs waxed won't conflict with that, instead it'll preserve the chambers as they were generated until the player is able to discover them.
this is likely intentional. why would oxidized ones be waxed?