I see a problem when the view-option "field names" is activated and indexes are
created or updated.
At the moment I'm not sure, what would be a satisfying solution, perhaps someone
else has a more exact idea:

When field names are shown in a document, the whole file may have more pages and
the index-entries may move to different pages. When creating or activating an
index while "field names" are checked in the view-menu, the page numbers of
indexes are based on the field-name-view that usually is not the view in which a
document will be printed or exported to pdf. 

Page preview shows the document without field names and so the page numbers in
indexes within the "page preview" do not match with the shown content.

One solution could be a message when creating or updating an index, like the
message "do you want to print the document with field names" when printing, so
that a user gets aware. If he doesn't, he might print a document with indexes
that point to wrong destinations.