Steps to reproduce the issue

This is a known Issue at TinyMCE but i wan't to report it here as its not an own Issue so far.

System information

• Nightly Build 4.0.0-alpha5-dev
• Multilingual Sample Data (French, German DE, Persian)
• Template: Cassiopeia
• macOS Sierra, 10.13.6
• Firefox 61 (64-bit)

CloudAccess.net

• PHP 7.1.15
• MySQLi 5.7.18-cll-lve