Link wrong generated

I tried a lot but can't find the problem.
On the (not public) website (www.ballet-heels.net) I have the module News Show Pro 2.3.1 running. After I changed the categories and setup News Show Pro just to display the newest article from each category the fourth link got an error.

The link ends with :fetish-art-exhibition
but should end with :fetish-art-exhibition&Itemid=216

&Itemid=216 at the end is missing and the result is different. Try and compare both links:
:fetish-art-exhibition
:fetish-art-exhibition&Itemid=216

I deleted the module and duplicated one of the three others but it doesn't helped. I deleted the category and created a new one but it doesn't helped. I deleted the articles and created new articles but it doesn't helped.
Now I don't know what's going on there! If you have an idea help me.

The links are probably generated through the Main menu settings. If I link an article or a category in the main menu the links in News Show Pro displayed articles at the home page are changed.
How can I stop it?

PS: mod_rewrite now activated.

It's perhaps more a bug of the K2!
Looks like the K2 component has this bug not only at my website.

More information: Item ID not assigned