QtCreator doesn't display custom PropertyEditor in some cases

I have a qml module MyModule and with a component MyComponent.

I have a MyComponentSpecifics file located withing property editor folder in qtcreator at MyModule/MyComponentSpecifics.qml.

I have a project that use this module and the project contains 2 files:

• MyDerivedComponent.qml : inherits MyComponent from MyModule and add some graphics
• main.qml : instanciates MyDerivedComponent

Use case #1 : I go in MyDerivedComponent.qml with designer, select the root node and can I see the custom property editor.
Use case #2 : I go in main.qml with designer and select the instance of MyDerivedComponent and can I see the custom property editor. NOK => the designer doesn't display the custom property editor but the generic one.