utf8mb4 warning keeps coming back up
I run CiviCRM 5.12.0 on Drupal 8.6.14 with PHP 7.2.15 and Apache2. I use postgres for my Drupal database, so the databases are split.
When I upgraded to the recent version that added the Mysql utf8mb4 check (5.12, I think), at the Drupal status page it began showing the message: "It is recommended, though not yet required, to configure your MySQL server for utf8mb4 support. You will need the following MySQL server configuration: innodb_large_prefix=true innodb_file_format=barracuda innodb_file_per_table=true." I added this configuration to my mysqld.cnf, and then restarted and saw that the message was gone. However, when I restarted my Apache server the next time, the message came back, and I found that the civicrm_utf8mb4_test table was present in the database and needed to be dropped. From code inspection, I concluded this could only come about as a result of a race condition with civicrm-core/Civi/Install/Requirements.php, where the table is created as a non-temporary table. So I changed that code to 'CREATE TEMPORARY TABLE ...' and 'DROP TEMPORARY TABLE ...', which caused the problem to go away.
However, my attempts to capture debug_backtrace() at this point in the code have all failed. I don't understand why that is. I tried printing it to the apache error log, as well as writing it to a file in '/tmp'. I have a dev version of the site, which uses the same CiviCRM database connection, so I also have disabled this site in my Apache configuration, as it seems like it could have been a complicating factor. The bug still occurs, with that original Civi/Install/Requirements.php.