执行squashmigrations后立即检测到模型变更的异常问题排查及修复方案咨询

我先跟大家说下我的操作流程和遇到的怪事：

首先执行python manage.py showmigrations查看当前迁移状态，输出如下：

mainapp
 [X] 0001_initial
...
 [X] 0240_employer_data
 [X] 0241_person_metadata
 [X] 0242_personemployer_employerworkplace
 [X] 0243_personemployer_employed_personemployer_stage
 [X] 0244_remove_employerworkplace_and_more

接着我运行了迁移压缩命令：

python manage.py squashmigrations mainapp 0244

之后再次用showmigrations查看状态，结果变成了：

mainapp
 [-] 0001_squashed_0244_remove_employerworkplace_and_more (244 squashed migrations) Run 'manage.py migrate' to finish recording.

但当我执行python manage.py migrate时，却收到了错误提示：

No migrations to apply.
Your models in app(s): 'mainapp' have changes that are not yet reflected in a migration, and so won't be applied.
Run 'manage.py makemigrations' to make new migrations, and then re-run 'manage.py migrate' to apply them.

这就让我完全摸不着头脑了——我刚做完迁移压缩，中间根本没改动任何内容，怎么会突然检测到模型有变更？

我又试了python manage.py makemigrations --dry-run，结果输出了一大堆类似这样的"Alter field"记录：

Migrations for 'mainapp':
  mainapp/migrations/0001_squashed_0244_remove_employerworkplace_and_more.py
    ~ Alter field field on employergroup
    ~ Alter field image_alt on employee
    ~ Alter field context on employer
    ...

我本来以为跑完squashmigrations之后，makemigrations应该显示"No changes detected"才对。

所以想请教各位：这到底是哪里出了问题？是什么导致了这种诡异的情况？我该怎么修复它呢？

备注：内容来源于stack exchange，提问作者Nils