Short version: the CMS crashes when you try to edit a block which has a PageReference property named ParentNode.

I'm upgrading an old project (from 6 R2 to newest version) and we're upgrading the old database. However since I have to change the name of ParentNode to something else, that property's data doesn't stick.

How to recreate:

1. Start a new EPiServer project. Select empty project. I used .NET Framework 4.7.1.
2. Create a block model inheriting BlockData that can probably be named anything you want.
3. Create a PageReference (or ContentReference) property named ParentNode.
4. Create the block. The CMS will just hang before it can ever load the block properties.

This is the blocktype I tested with:

[ContentType(
DisplayName = "Page List Block",
GUID = "9cb392be-3a46-40ea-99fd-a1b0c551eea7"]
public class PageListBlock : BaseBlock
{
    Display(
    Name = "Parent node",
    Description = "Parent page of the pages to be listed",
    GroupName = SystemTabNames.Content,
    Order = 100)]
    public virtual PageReference ParentNode { get; set; }
}

Any suggestions as to why this happens?

EDIT: This happens in two entirely different projects, so it's not a one-off thing.