We've misused sqlite3_column_name. The SQLite documentation states that the following:

The returned string pointer is valid until either the prepared statement is destroyed by sqlite3_finalize() or until the statement is automatically reprepared by the first call to sqlite3_step() for a particular run or until the next call to sqlite3_column_name() or sqlite3_column_name16() on the same column.

As part of our query_by_name infrastructure we've first received all field names for the prepared statement and stored them as string slices for later use. After that we called sqlite3_step() for the first time, which invalids the pointer and therefore the stored string slice.