@Xristoph cRad

K2 menu settings apply only when you select more than one K2 category. This is the intended behavior. If you select a single category then the settings are inherited from the category edit page and the menu link settings are disabled. If this does not cover your needs there are other ways to achieve what you need. You can either create one more K2 category ( it can be empty ) and select both in the menu link. An of course you can always use modules and apply your own styles.

I am experiencing the same problem, but it is not working as you state.
I've just downloaded version 2.6.8
installed on joomla 2.5.18 that is running a gantry template.
The K2 latest list Menu Item has only one Category selected and it is ignoring the settings in the category that are set to 3 columns. If I set the menu item setting to multiple columns it only displays in one column, to width of the relevant column. eg. 2 column displays, 1 column at 50% width.

@mik

What i wrote refers to the categories list menu links, not in latest items menu links.