subtract(years) causes incorrect date when crossing historical timezone change in Malaysia

[liangpishu]

Describe the bug
When parsing a date in 2081 and subtracting 100 years to get a date in 1981, the resulting date is incorrect (shifts from Dec 25 to Dec 1, a 24-day difference). This only happens in Malaysia timezone and appears to be related to Malaysia's historical timezone change on December 31, 1981 (UTC+7:30 → UTC+8:00).

Expected behavior
After subtract(100, "years"), the date should be 1981-12-25 (same day and month as the original date).

Information

• dayjs version: 1.11.19
• Plugins: customParseFormat, utc, timezone
• Timezone: Asia/Kuala_Lumpur (UTC+8, but was UTC+7:30 before Jan 1, 1982)
• Node.js version:v20.19.3
• OS: macOS

[liangpishu]

const dayjs = require('dayjs');
const customParseFormat = require('dayjs/plugin/customParseFormat');
const utc = require('dayjs/plugin/utc');
const timezone = require('dayjs/plugin/timezone');

dayjs.extend(customParseFormat);
dayjs.extend(utc);
dayjs.extend(timezone);

// Parse date in year 2081
const parsed = dayjs("20811225", "YYYYMMDD");
console.log("Step 1 - Parsed:", parsed.format("YYYY-MM-DD"), "date():", parsed.date());
// Output: 2081-12-25, date(): 25 ✅

// Subtract 100 years
const subtracted = parsed.subtract(100, "years");
console.log("Step 2 - After subtract:", subtracted.format("YYYY-MM-DD"), "date():", subtracted.date());
// Expected: 1981-12-25, date(): 25
// Actual: 1981-12-01, date(): 1 ❌

// Compare: Direct parsing of 1981 date works correctly
const direct = dayjs("19811225", "YYYYMMDD");
console.log("Direct parse 1981:", direct.format("YYYY-MM-DD"), "date():", direct.date());
// Output: 1981-12-25, date(): 25 ✅