Steps to reproduce the issue

New install of Joomla 3.7.5 no sample data
Add 2 new users through administrator (both as 'registered')
Add new menu item to main menu for 'Edit User Profile'
In front end login as 1st new registered user
Go to Edit User Profile Page
Change email address and confirm email address to the 2nd registered user
Click Submit
You see the warning message 'The email address you entered is already in use or invalid. Please enter another email address.' - This is expected
Now click Home (to go away from the profile page)
Click Edit User Profile in menu
Page is now populated with the email address previously submitted but rejected

Expected result

Once the new email address has been rejected, it should be cleared from the cache, if the user misses the warning message, and then return to the user profile page, it looks like the email was successfully changed even though it wasn't.

Actual result

Returning to the user profile page shows the rejected email address of the other user

System information (as much as possible)

Database Version 5.6.37-log
Database Collation utf8_general_ci
Database Connection Collation utf8mb4_general_ci
PHP Version 5.6.31
Web Server Apache
WebServer to PHP Interface cgi-fcgi
Joomla! Version Joomla! 3.7.5 Stable [ Amani ] 14-August-2017 12:09 GMT
Joomla! Platform Version Joomla Platform 13.1.0 Stable [ Curiosity ] 24-Apr-2013 00:00 GMT
User Agent Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:55.0) Gecko/20100101 Firefox/55.0

Additional comments

This is a usability issue