Convert pages issue with CategoryList

Description

Steps to reproduce

1. Trying to convert old page types to new page type. Create a page type that has a CategoryList property and input some value for this property. For example:

    [ContentType(DisplayName = "OldPage", GUID = "b09da6de-6ab5-44d5-a764-4a7f7edbf0d8", Description = "")]
    public class OldPage : SitePageData
    {
        [CultureSpecific]
        [Display(            
            GroupName = SystemTabNames.Content,
            Order = 1)]
        public virtual CategoryList ListOld { get; set; }
    }

2. Create another page type which also has CategoryList property.

 [ContentType(DisplayName = "NewPage", GUID = "07790693-f22e-4278-9a1d-b1c0e342f173", Description = "")]  
 
  public class NewPage : SitePageData
    {
        [CultureSpecific]
        [Display(
            GroupName = SystemTabNames.Content,
            Order = 1)]
        public virtual CategoryList ListNew { get; set; }

3. Convert from OldPage to the NewPage.

Expected:
The categories are copied.

Actual:
The categories are not copied across.