Just tried creating a newsletter with name Main_Page1231235 and see what I got on Special:CreateNewsletter
Got this:
[Bug56269] Exception thrown with an uncommited database transaction: [d1d448271182417d2db6c833] [no req] MWException from line 129 of /var/www/core/core/extensions/Newsletter/includes/content/NewsletterContent.php: Cannot find newsletter with name \"Main Page1231235\" [DBQuery] my_wiki ROLLBACK /* MWExceptionHandler::rollbackMasterChangesAndLog */ [exception] [d1d448271182417d2db6c833] [no req] MWException from line 129 of /var/www/core/core/extensions/Newsletter/includes/content/NewsletterContent.php: Cannot find newsletter with name \"Main Page1231235\"
Possible GCI task, and its an easy fix afaik!