Wrong explaination of addPlugin
Hallo Core Team,
in ExtensionManagerUtility at addPlugin you wrote:
@param array $itemArray Numerical array:  => Plugin label,  => Underscored extension key,  => Path to plugin icon...
Of cause array key 1 could be the extension key, but one extension can provide multiple plugins and in that case you need something to differ.
It's the value which will be stored in column CType (or list_type). It's more a plugin name or a content element identifier. Further you have the extensionName as third parameter already. So it does not make sense to define ExtKey twice.