Thank you for reporting this problem.
I logged it for fixing in our PITS system and updated your Telerik points. Here you can find the PITS Issue: Public URL
The solution that you can currently use is to set the ToolbarMode property to Default
in the \Program Files\Common Files\Microsoft Shared\Web Server Extensions\wpresources\RadEditorSharePoint\18.104.22.168__1f131a624888eeed\Resources\ConfigFile.xml and ListConfigFile.xml files
the Telerik team
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