CollectionEditor does not display XHtml editor in dialog correctly

Description

Steps to reproduce

1. Use an alloy site.

2. Add the following new page type

    [ContentType]
    [AvailableContentTypes(Availability.All)]
    public class CollectionEditorPage : PageData
    {
        [EditorDescriptor(EditorDescriptorType = typeof(CollectionEditorDescriptor<NewsItem>))]
        [Display(Name = "News Items", Order = 200)]
        public virtual IEnumerable<NewsItem> Test { get; set; }
 
    }
 
    [PropertyDefinitionTypePlugIn]
    public class NewsItemList : PropertyList<NewsItem>
    {
        public override PropertyData ParseToObject(string value)
        {
            ParseToSelf(value);
            return this;
        }
 
        protected override NewsItem ParseItem(string value)
        {
            return JsonConvert.DeserializeObject<NewsItem>(value);
        }
    }
 
    public class NewsItem
    {
        [CultureSpecific]
        [Required]
        public virtual XhtmlString Content { get; set; }
    }

3. Create a new page of the above mentioned page type.
4. Click the plus to open the collection editor dialog.

Expected:
To see the xhtml editor displayed correctly

Actual:
The styles drop down does not include the custom styles, and parts of the editor are not visible within the dialog.