Bug - Too Much Text

Steps to Reproduce

Create a new blank doucment
Insert the text "My heading 1"
Format this text with the built-in "Heading 1" style
Press Enter twice,
On the References tab, click on "Cross-reference".
Change the reference type to "Heading".
Press Insert to insert a cross reference.

Put your cursor at the start of the heading (infront of the word "My").
Press Enter to add a new paragraph above the heading.
Insert the text "new paragraph".

On the Insert tab, click Bookmark.
Select the bookmark and press GoTo.
You can see that the bookmark includes this extra paragraph.

Right mouse click on the cross reference and press Update Field.
You will see that the cross reference text has updated to include the extra paragraph.

Solution - Move the Cursor Before

When you need to add text to an existing cross reference position the cursor at least one character from the end.
Type in you additional text and then delete the unwanted character.

Important

Word does not use a multi-level list for its "default" heading styles so we need to create a new multi-level list.
To fix an existing broken cross reference you will have to redefine the bookmark.