Steps to reproduce the issue

Step 1. Log in at the front page with Super Admin
Step 2. Open the article and edit some, Then, save the page
Step 3. Save, but the Warning made me unsaved the article

I tried JCE and TinyMCE with different templates but no sucess. The exception is smartphone. I can save it with smartphone, but with PC I can not save it.

Expected result

The article should be saved successfully.

Actual result

Warning: Empty solution not allowed

System information (as much as possible)

Joomla 3.7.2
PHP 7.1

Additional comments

Joomla captcha plugin is producing this bug. IF it is set to OFF, there is no issue. The captcha plugin is doing something wrong on article page.