the ...-unload-hook convention doesn't work

[Luc Teirlinck]

Dave Love wrote:

    I'm confused by this, since I'm sure it worked when I implemented it,
    but the installed code never seems to have been right since it's
    calling a function as if it were a hook list.

It now is supposed to be a normal hook.  From (elisp)Unloading:

     If `FEATURE-unload-hook' is defined, it is run as a normal hook
     before restoring the previous definitions, _instead of_ the usual
     hook-removing actions.

But how could this have broken things?  `run-hooks' is supposed to be
able to handle a single function instead of a list, so there should be
no problems with compatibility in as far as line 143 is concerned.
Are there concrete examples of problems arising from either defining
FEATURE-unload-hook as a function (even though, according to the Elisp
manual, this is now considered obsolete) or defining it as a normal
hook?

Sincerely,

Luc.