You might want to look into this, but there seems to be a bug where despite being superglued to the rest of the train, blocks from DnD would vanish from certain parts of the train when it's disassembled and brought back to edit/build mode.

here's proof

assembled

disassembled:

I'm not the only one experiencing this. others experience this every time they assemble and then disassemble trains with those parts installed.

the headlamp uses the brass lamp from this mod and when the train is disassembled, the lamp disappears despite being superglued