The buttons from "Content" wiki toolbar text box don't work when editing in Object mode

Steps to reproduce

1. Edit a page in Objects mode
2. Search and add the PanelClass xobject 
3. In the 'Content' text box, add some text (few words)
4. Select a word and click the  'Bold' button or any other button from the toolbar

Expected results

The buttons work (e.g. an action is performed after clicking each button).

Actual results

Nothing happens. Also there are no errors in JS console.

It is to be mentioned that the buttons from the 'Description' text box wiki toolbar placed above are working properly.

The issue was reproduced also on XWiki 17.4.7.