The hint that is displayed if the mouse gets moved over a MailMergeField is not
updated after changing the DataColumnName via the API.

Use the following steps to reproduce the bug:

1) create a new writer document

2) insert a mailmergefield (Ctrl+F2) - for example one that references
Bibliography.biblio.Address

3) move the mouse over the new inserted mailmergefield and you will get the
following hint: "Bibliography.biblio.Address"

4) now run the followin macro:

	xenum = ThisComponent.TextFields.createEnumeration() 
	f = xenum.nextElement()
	f.TextFieldMaster.DataColumnName = "MyAddress"
	f.update

5) again, move the mouse over the mailmergefield and you will see, that the hint
 hasn't been updated, whereas the display of the field itself shows the new
Columnname "<MyAddress>" . 

After saving and reopening the document, the field is still displayed as
"<MyAddress>" and the hint is correct then, too.