I am not sure if WebDataMenu was a new control in v11.1, but it seems really buggy. 

I added 4 root menu items and made the third root menu item have 2 child menu items.  The 4th item does not show up - there seems to be space for it, but hovering or clicking does nothing and the words for the menu item do appear to show up at all.

Also when I try to reduce the font using the webdatamenu property Font-size, the any of the other CssClass properties available at different levels, the font size (and also color) do not change.

Additionally I wanted to change the height of the menu "bar" and this did shrink to the appropriate size, but the text stayed in the same position it was in before and I could find no way to get it to shift so that it was no longer partially "cut off".  Also there is now a "gap" between the 3rd root menu item and its children.

Any help with this would be much appreciated.