Take a look at #1084. Yes, I know it's silly. Yes, I know its final resolution was "won't fix". I even lowered its priority to 1 as it was back in the day.
But please bear with me: I thought that after all these years a fix could be found which doesn't imply to add code for specific shapes. If it isn't the case feel free to close this one, no questions asked.
If the volume of the shape was increased larger than a barrel can hold, that would be a workaround. The downside is instead of showing the red X the DOS game uses, it would say Won't Fit.
Are there any other shapes that have this restriction?
Anything that shouldn't go inside a container because anything movable and lit has a "Usecode events" flag on it in ES. Perhaps it would be worthwhile to check this? The special items from The Silver Seed also seem to have this flag checked, and changes when equipping / unequipping them work as expected.
Next snapshot fixes this.
In SI, the way it won't light in the belt/waist slot is via a check in this code:
void checkLightSourceSpent 0x98A (var unlit_shape, var lit_shape)