Strange behavior: nav mod_customnav transformed into mod_sitemap

Hello, I would recreate this structure
Header
- div.preHeader
- div.mainHeader
--- nav

I've create a custom Html module:

<div id="mainHeader">
{{insert_module::1}}
{{insert_module::8}}
{{insert_module::26}}
</div>

And inserted it into header column in "Structure" page. The module 26 is Nav
I've done this for wrap the nav into div.mainHeader, instead of put it directly into HEADER tag.
I've expected to find a nav.mod_customnav block, but I find a div.mod_sitemap block instead...

If I put the nav module directly into header column I obtain the generated nav.mod_customnav... but the target is to create a DIV as row inside HEADER
Someone can help me or explain this behaviour?
Thank you

I can not confirm this. If 26 is a navigation you get

HTML Code:

---

<nav class="mod_navigation block">

---

If it is a sitemap you get

HTML Code:

---

<div class="mod_sitemap block">

---

I you want to have a wrapper for some modules you also can build two HTML modules. One with

HTML Code:

---

<div id="mainHeader">

---

Name it "Wrapper open"
and one with

HTML Code:

---

</div">

---

Name it "Wrapper close".
Include those into your page layout.

Thank you for this solution!
I appreciate it for creating various horizontal sections with modules inside and put all of them into header or footer.