I found that base-richtext.js
is missing latest fixes merged into core.
So, I would like to make this work without overriding core files, to prevent such issues in future.
The only part I'm not sure about is
this.customTags = Object.keys(eZ.richText.customTags).filter(this.isEnabled).filter((key) => !eZ.richText.customTags[key].isInline);
this.inlineCustomTags = Object.keys(eZ.richText.customTags).filter(this.isEnabled).filter((key) => eZ.richText.customTags[key].isInline);
I didn't cover this, but I see it works fine without this change.