Custom profile field : uppercase letter in short name blocks the notification page

Hi,

We discover a bug when we use uppercase text in custom profile field. 

Here are some information to view this bug.

1. Go to "user profile fields" page
2. Create a new profile field (for example text)
3. Add a short name and use at least one uppercase in the text (see screenshot) 
4. Add name and save
5. Go to "Notifications" page. You are redirected and blocked on admin/upgradesettings.php page with authentification plugin option. (see screenshot) 

If you delete uppercase in the short name of the profile field, "Notifications" page works again.

(PS : test with php 7.2 and mysql 5.7)

Best regards