Duplicative index entries in v10/HEAD builds

In 9.6, the HTML doc build's index entry for "data type" looks like

data type, Data Types
base, The PostgreSQL Type System
category, Overview
composite, The PostgreSQL Type System
constant, Constants of Other Types
conversion, Type Conversion
enumerated (enum), Enumerated Types
internal organization, Base Types in C-Language Functions
numeric, Numeric Types
type cast, Type Casts
user-defined, User-defined Types

where each of the phrases on the right is a hyperlink to a section.
Fine. But in HEAD we get

data type, Data Types, Numeric Types, Enumerated Types, Domain Types, Type Conversion, The PostgreSQL Type System, The PostgreSQL Type System, The PostgreSQL Type System, Polymorphic Types, Base Types in C-Language Functions, User-defined Types
base, The PostgreSQL Type System
category, Overview
composite, The PostgreSQL Type System
constant, Constants of Other Types
container, The PostgreSQL Type System
conversion, Type Conversion
domain, Domain Types
enumerated (enum), Enumerated Types
internal organization, Base Types in C-Language Functions
numeric, Numeric Types
polymorphic, Polymorphic Types
type cast, Type Casts
user-defined, User-defined Types

How do we get rid of those duplicative (and not-appropriate-to-the-
main-topic) links on the first line?

v10 has the same disease, though not quite as bad as HEAD
because I just added some more <indexterm> items in HEAD.

regards, tom lane