Почему конфигурация Apache SPA mod_rewrite использует точку в регулярном выражении, а курсор приводит к сбою Apache?

Question

Типичная конфигурация Apache SPA на основе mod_rewrite:

DocumentRoot "${webDir}"

<Directory "${webDir}">
  LogLevel rewrite:trace8

  RewriteEngine On
  RewriteCond %{SCRIPT_FILENAME} !-f
  RewriteRule . index.html [L]
</Directory>

Если я заменю регулярное выражение последнего правила на знак вставки:

  RewriteRule ^ index.html [L]

Apache segfaults on http://localhost/(работает с любым непустым путем). Журнал ошибок не вызывает подозрений:

[rewrite:trace3] mod_rewrite.c(493): strip per-dir prefix: /home/user/work/out/ -> 
[rewrite:trace3] mod_rewrite.c(493): applying pattern '^' to uri ''
[rewrite:trace4] mod_rewrite.c(493): RewriteCond: input='/home/user/work/out/' pattern='!-f' => matched
[rewrite:trace2] mod_rewrite.c(493): rewrite '' -> 'index.html'
[rewrite:trace3] mod_rewrite.c(493): add per-dir prefix: index.html -> /home/user/work/out/index.html
[rewrite:trace2] mod_rewrite.c(493): strip document_root prefix: /home/user/work/out/index.html -> /index.html
[rewrite:trace1] mod_rewrite.c(493): internal redirect with /index.html [INTERNAL REDIRECT]

Лог с точкой (который не приводит к сбою) выглядит так:

[rewrite:trace3] mod_rewrite.c(493) strip per-dir prefix: /home/user/work/out/ -> 
[rewrite:trace3] mod_rewrite.c(493) applying pattern '.' to uri ''
[rewrite:trace1] mod_rewrite.c(493) pass through /home/user/work/out/
[rewrite:trace3] mod_rewrite.c(493) strip per-dir prefix: /home/user/work/out/index.html -> index.html
[rewrite:trace3] mod_rewrite.c(493) applying pattern '.' to uri 'index.html'
[rewrite:trace4] mod_rewrite.c(493) RewriteCond: input='/home/user/work/out/index.html' pattern='!-f' => not-matched
[rewrite:trace1] mod_rewrite.c(493) pass through /home/user/work/out/index.html