The collection property is implemented as

[Category( SmfAttrTypeText.ISmfPageControl.AllVisConfigPageSpecs.Category )]
[Description(
SmfAttrTypeText.ISmfPageControl.AllVisConfigPageSpecs.Description )]
[DesignerSerializationVisibility( DesignerSerializationVisibility.Content )]
public PageSpecCollection AllVisConfigurablePageSpecs
{
  get
  {
     return this.Runtime.AllVisConfigurablePageSpecs;
  }

 // leaving out this set accessor causes the code deserialization to
work!!!
  set
  {
     this.Runtime.AllVisConfigurablePageSpecs = value;
  }
}

and the custom collection class as

public class PageSpecCollection : CollectionBase
{
public PageSpecCollection()
{
}
public PageSpecCollection ( PageSpecCollection value)
{
this.AddRange(value);
}
public PageSpecCollection( PageSpec[] value)
{
this.AddRange(value);
}
public int Add(PageSpec value)
{
return this.List.Add(value);
}
public void AddRange(PageSpec[] value)
{
if (value == null)
{
throw new ArgumentNullException("value");
}
for (int index = 0; index < value.Length; index++)
{
this.Add(value[index]);
}
}
public void AddRange(PageSpecCollection value)
{
if (value == null)
{
throw new ArgumentNullException("value");
}
int cnt = value.Count;
for (int index = 0; index < cnt; index++)
{
this.Add(value[index]);
}
}
public bool Contains(PageSpec value)
{
return this.List.Contains(value);
}
public void CopyTo(PageSpec[] array, int index)
{
this.List.CopyTo(array, index);
}
public int IndexOf(PageSpec value)
{
return this.List.IndexOf(value);
}
public void Insert(int index, PageSpec value)
{
this.List.Insert(index, value);
}
public void Remove(PageSpec value)
{
this.List.Remove(value);
}
public PageSpec this[int index]
{
get
{
return (PageSpec) this.List[index];
}
set
{
this.List[index] = value;
}
}

The strange thing is that meanwhile I found out that leaving out the set
accessor of the collection property causes the code deserialization to work.
But I cannot imagine why.

"System.ComponentModel.Design.Serialization.CollectionCodeDomSerializer",