Symptom
Re-translating an already-translated title defeats the boilerplate stripper and leaves residue.
Fix
Re-translation and recomputation always start from the source (title_en, not title_ko).
The trap
A _ko field often hides in the source fallback: description or description_ko. When the source is missing, you re-translate the display translation (Korean → Korean). Fixing one field is not enough; check every sibling field's fallback for a display copy.
Why this bites non-ASCII users
If your product runs in a non-English market, you carry two copies of every text field: the original (usually English) and the localized display copy. Any pipeline that "helpfully" falls back to whichever is present will eventually feed the localized copy back into the translator. English-only shops don't have this failure mode. You do.