PL/SQL Error 323 in form from package subclassed from object group in object library

I have encountered PL/SQLError 323, for example:

"Compilation error on package body LOC_SET_DISPLAY_ITEMS:

PL/SQL ERROR 323 at line 78, column 14

subprogram or cursor 'CLEAR_HR_DISPLAY_ITEMS' is declared in a package specification and must be defined in the package body"

in a number of forms, both in 11g and 12c.

The package specification and package body are subclassed from an object group in an object library. 

When I look at the package body code from the object library, the "missing" procedure is there.

When I look at the package body code in the form, the procedure is not to be found.