Why did a merged heading fill an unrelated later row?

import {DatabaseSync} from 'node:sqlite';
import {TextDecoder} from 'node:util';
import {inflateSync} from 'node:zlib';
import {posix} from 'node:path';
import {createHash} from 'node:crypto';
const rows=(db,sql)=>db.prepare(sql).all().map(r=>({...r}));
const failed=(action)=>{try{action();return null;}catch(e){return {code:e.errcode??e.code??e.name};}};

import assert from 'node:assert/strict';
const run=function run(i,corrected=true){
    const output=[];let carried=null;
    for(const row of i.rows){
      const own=i.cells.find(c=>c.row===row&&c.col===i.column);
      if(own)carried=own.value;
      if(!corrected){output.push({row,value:carried});continue;}
      const merge=i.merges.find(m=>row>=m.fromRow&&row<=m.toRow&&i.column>=m.fromCol&&i.column<=m.toCol);
      const anchor=merge?i.cells.find(c=>c.row===merge.fromRow&&c.col===merge.fromCol):null;
      output.push({row,value:own?own.value:anchor?anchor.value:null});
    }return output;
  };
const cases=[{"label":"misleading base","input":{"column":1,"rows":[2,3,4],"cells":[{"row":2,"col":1,"value":"North"}],"merges":[{"fromRow":2,"toRow":3,"fromCol":1,"toCol":1}]},"expected":[{"row":2,"value":"North"},{"row":3,"value":"North"},{"row":4,"value":"North"}],"corrected":false},{"label":"corrected base","input":{"column":1,"rows":[2,3,4],"cells":[{"row":2,"col":1,"value":"North"}],"merges":[{"fromRow":2,"toRow":3,"fromCol":1,"toCol":1}]},"expected":[{"row":2,"value":"North"},{"row":3,"value":"North"},{"row":4,"value":null}],"corrected":true},{"label":"column outside merge","input":{"column":2,"rows":[2,3],"cells":[{"row":2,"col":1,"value":"North"}],"merges":[{"fromRow":2,"toRow":3,"fromCol":1,"toCol":1}]},"expected":[{"row":2,"value":null},{"row":3,"value":null}],"corrected":true},{"label":"no merged range","input":{"column":1,"rows":[2,3],"cells":[{"row":2,"col":1,"value":"North"}],"merges":[]},"expected":[{"row":2,"value":"North"},{"row":3,"value":null}],"corrected":true}];
for(const test of cases){
  const actual=run(test.input,test.corrected);
  assert.deepEqual(actual,test.expected,test.label);
  console.log(test.label,actual);
}