Macro parameters with suggest pickers can't be set when editing existing pages with the WYSIWYG editor

The user picker (or page picker or any other similar picker) won't display properly when trying to add a macro that uses it inside a page. You start typing the user and no suggestions are prompted.

To reenact this bug, one has to create a page, save it and then edit it in form mode. 

Adding the macro during the page creation works, adding the macro while editing the page in wysiwyg mode works, adding the macro within the wysiwyg of a single property works.