I recently had a small issue with every wordpress blog I host on my dedicated EC2 cluster (Mysql + nginx + php) : The « Publish » button was missing.
There only was a « Submit to review » button , but nothing else !
After some investigation, It looks like the mysql db was involved.
The problem was two conf options in sql_mode from /etc/my.cnf : NO_ZERO_DATE and NO_ZERO_IN_DATE
If you want to know what those options are made for, take a look there