The preamble macro is, I believe, not part of core but special for
tiddlywiki.com along woth a bunch of other
documentation macroscould it be that you've copied e.g the full
tiddlywiki.com and in those copies it's working but if you try it on what was originally an empty tw, then it doesnt?
Do an advanced search (magnifying glass next to search field) for preamble and see what shows up under system/shadow in your various TWs.
<:-)
.