Smallworld ignores data from FME that is destined for text_join fields.
Smallworld has a data type called "text_join" which allows you to store a string of indefinite length on a Smallworld record. Under the hood, this data type is actually modeled as a join relationship to an internal table that stores chunks of finite-length strings that can be added to each other to emulate an indefinite-length string. So a text_join is actually considered a join field and not a physical field.
This becomes a problem when you want to copy data into one of these text_join fields. This is not an unusual requirement. Many Smallworld objects have at least one text_join field (e.g., Electric Office objects have a "Remarks" field; other datamodels might have a "Comments" field). Not being able to import attribute values via FME into those Smallworld objects is not an insignificant limitation.
I raised a case with GE about this recently and was told that this was a duplicate of a same case that I had raised a few years ago. I knew that there had been something familiar with this issue, but I couldn't remember that I had already encountered it a few years ago. Because there is no patch in sight any time soon for this issue, I present to you the fix I made. Like most of the FME/Magik tweaks I have had to make, the implementation is fairly easy.
(click on image to enlarge)