Yes, that is the cause of the error you are getting.
I don’t know phpMyAdmin well, especially not from a open-source development perspective. Perhaps some elements are created on a form submit or something? Without a reproducible test case in front of me, I can only speculate.
phpMyAdmin uses HTML forms and PHP, so it could conceivably be affected by this PHP issue. It isn’t related to inserting (in a database sense) anyway - it is to do with the how PHP creates variables in a POST operation (e.g. in a form submission).
Definitely not - a database structure should not be dictated by a bug in a development tool. The bug needs to be found and resolved, or the tool needs to be changed.
As I say, I will need a reproducible test case to help further. I suggest you create a database export that someone could load into their own database in order to examine the issue further. Please add detailed, step-by-step bug reproduction instructions also.
Looks like several folks have had issues with phpMyAdmin with this setting.