[TYPO3-english] HMENU typoscript ACTIFSUB renders an empty li in one rootline

[Domi]

Hello,

I am stuck with a weird menu rendering problem in TYPO3 4.7.4.

The ACTIFSUB renders an empty <li></li> in the rootline of subpages with 
directory = 9. In all other subpages it works as expected.

How can I track down what happens here? This is the menu:

menu.mainNavigation = COA
menu.mainNavigation.wrap = <div class="navigationWrap"><nav>|</nav></div>
menu.mainNavigation.10 = HMENU
menu.mainNavigation.10 {
   entryLevel = 0
   wrap  = <ul id="menuMain">|</ul>
   1 = TMENU
   1 {
     expAll = 0
     noBlur = 1

     NO = 1
     NO.allWrap = <li class="normal">|</li>

     ACT < .NO
     ACT.allWrap =  <li class="active">|</li>

     IFSUB < .NO
     IFSUB.allWrap = <li class="sub">|</li>

     ACTIFSUB < .NO
     ACTIFSUB.allWrap = <li class="active sub">|<li>

     CUR < .NO
     CUR.allWrap = <li class="current">|</li>

     CURIFSUB < .NO
     CURIFSUB.allWrap = <li class="current sub">|</li>

   }
}

menu.mainNavigation.20 = COA
menu.mainNavigation.20.wrap = <div class="subNav">|</div>
menu.mainNavigation.20.10 = HMENU
menu.mainNavigation.20.10 {
   special = directory
   special.value = 9
   wrap = <ul>|</ul>
   1 = TMENU
   1 {
     expAll = 0
     noBlur = 1
     NO = 1
     NO {
       linkWrap = <li>|</li>
     }
   }
}
menu.mainNavigation.20.20 < menu.mainNavigation.20.10
menu.mainNavigation.20.20.special.value = 10
menu.mainNavigation.20.30 < menu.mainNavigation.20.10
menu.mainNavigation.20.30.special.value = 11


Here the output:
<ul id="menuMain">
<li class="active sub"><a href="index.php?id=9">Link 1</a></li>
<li></li>
<li class="sub"><a href="index.php?id=10">Link 2</a></li>
<li class="sub"><a href="index.php?id=11">ZLink 3</a></li>
<li class="normal"><a href="index.php?id=15">Link 4</a></li>
<li class="normal"><a href="index.php?id=16">Link 5</a></li>
<li class="normal"><a href="index.php?id=1">Link 6</a></li>
</ul>

Thanks for any hint,

Cheers,

Dominic