Indentation changes rendering of <pre>

The following code with indentation enabled renders a line break before the closing </pre>:

    <div><p>some doc ..............................</p>
     <pre><code><span>some code of just the right length ....</span></code>
     </pre><p>some more doc</p>

This adds an extra blank line to the pre element, which renders differently whether indentation is enabled or not.

open Tyxml.Html

let content =
  html
    (head (title (txt "example")) [])
    (body
       [
         div
           [
             div
               [
                 div
                   [
                     p [ txt "some doc .............................." ];
                     pre
                       [
                         code
                           [
                             span
                               [ txt "some code of just the right length ...." ];
                           ];
                       ];
                     p [ txt "some more doc" ];
                   ];
               ];
           ];
       ])

let () =
  Format.printf "%a" (pp ~indent:true ()) content

Start by running the provided OCaml example with pp ~indent:true and compare its output with indentation disabled. Trace the pretty-printer entry point used by pp; the issue is done when indentation no longer adds a blank line before the closing pre element.