Iam unable to save custom properties . In my SitePageBase , iam placing two custom properties 

1.  [Display(
Name = "Page testing",
Description = "Select multiple pages",
GroupName = SystemTabNames.PageHeader,
Order = 28)]
public virtual PageReference pagetesting { get; set; }

2.   // [AllowedTypes(typeof(TagPage))]
[Display(Name = "Links", Description = "", GroupName = SystemTabNames.PageHeader, Order = 260)]
public virtual LinkItemCollection Links { get; set; }

Iam able to change ,select and save the first one , but not other . Please help me . Whether iam missing anything  explicitly .