This is an issue I've ran into when trying to convert specifics from group mapping to table driven, now I'm running into with SLA set by subcategory.
The behavior I get for both specifics and SLA set by incident subcategory is that it works well when using the smart classify to select subcategory but when I use the regular dropdowns for service > category> subcategory the correct subcategory ID/specifics form/subcategory SLA name will not populate.
I'm building off an older content system that still uses group mapping for specifics at the moment (pre 8.0 maybe pre 7.0) anyone have any idea what's causing the dropdown service classification to behave differently ?
Smart classify uses a Related Item Picker to directly populate a relationship onto the Subcategory ID, so the relationship always loads when used this way.
However on older content, the subcategory ID value didn't autopopulate from subcategory when changed, meaning this relationship wouldn't be built if manually filled out vs smart classify, thus any customization you've done based on subcategory may not load when filling it in via the dropdown values.