Status line not updated at once when changing User highlight groups dynamically

[lifepillar]

The following is contrived code that modifies a highlight group in the status line according the current mode (Normal or something else):

fun! SetMode()
  execute 'hi! link XYZ' (mode() ==# 'n' ? 'Search' : 'Visual')
  return ''
endf

fun! BuildStatusLine()
  return '%{SetMode()}%#XYZ# MODE %*'
endf

set statusline=%!BuildStatusLine()

The above works as I expect (colors change immediately when switching to and from Normal mode). Now, try using a User highlight group instead:

fun! SetMode()
  execute 'hi! link User1' (mode() ==# 'n' ? 'Search' : 'Visual')
  return ''
endf

fun! BuildStatusLine()
  return '%{SetMode()}%1* MODE %*'
endf

set statusline=%!BuildStatusLine()

I would expect this to behave the same as before, but it seems that the status line is not refreshed immediately after switching mode (if I press another key, the status line is updated). I know that this is a minor issue, but shouldn't the two snippets above behave in the same way?

I can reproduce this with Vim 8.1.950 and vim --clean.

[dylnmc]

I haven't tested it recently, but I don't think any of the built-in's work (such as the ones listed in :help 'hi'). I think they are expected to remain more static. Luckily, user-defined highlight groups work.