Keep Coding

I'm using Tim Pope's repeat.vim plugin and am having some trouble invoking repeat#set correctly. I want to create two mappings for quickly navigating between sections of a help doc, which are delineated by rows of equals signs. My function for going to the next section below works and is repeatable.
function! s:NextHelpSection()
execute "normal /^===\<CR>"
nohlsearch
normal zt
endfunction
nnoremap <buffer> <silent> <LocalLeader>n
\ :<C-u>call <SID>NextHelpSection()<CR>
\:<C-u>call repeat#set("\<LocalLeader>n")<CR>
My function for going to the previous section works on its own but fails when I try to repeat it with E21: Cannot make changes, 'modifiable' is off.
function! s:PrevHelpSection()
execute "normal ?^===\<CR>"
nohlsearch
normal zt
call repeat#set("\<LocalLeader>p")
endfunction
nnoremap <buffer> <silent> <LocalLeader>p :<C-u>call <SID>PrevHelpSection()<CR>
The difference between the two is just where I call repeat#set, whether it's inside the function or afterwards. Why should this matter? Why would this second version fail? It's cleaner, so I'd prefer to write it this way if possible.