If you tried to use Infragistics classic UltraWebMenu control in IE9 you may experience issue (even in the latest version, 11.2 at the time of this post) whereby menu items don’t change background on mouse hover even though background is specified in menu’s HoverItemStyle property.

The solution is specify BorderStyle in HoverItemStyle. It can be any value besides NotSet, but the actual attribute has to be there. So for example if you want your hover style to have no borders and your original style looks like:

<HoverItemStyle
   ForeColor="White" 
   BackColor="#81C0E9"
   Height="18px"
   BorderWidth="0px"> 
</HoverItemStyle>

change it to

<HoverItemStyle
   ForeColor="White"
   BackColor="#81C0E9"
   Height="18px"
   BorderWidth="0px" 
   BorderStyle="None">
</HoverItemStyle>

I don’t know why border style affects showing of the background, but there you have it. Adding BorderStyle to HoverItemStyle will enable displaying of background color on hover.