There is a solution, but i suspect without themes support, however this could be fixed also.
As i found there problem within background-image of hovered styles
So i redefined them to these:
.RadTreeView_Default .rtHover .rtIn
{
color#000;
border-color: #c4c4c4 #b5b5b5 #9e9e9e;
background-color: #e1e1e1;
background-image:none !important;
}
.RadTreeView_Default .rtSelected .rtIn
{
color:#fff;
border-color: #8d8d8d #7e7e7e #6c6c6c;
background-color: #959595;
background-image:none !important;
}
Ofcource there is no nice background now, but if u defined these styles for IE8 and include them on the page itself but not CSS, this will not affect other browsers:
<!--[if IE 8]>
new styles go here
<![endif]-->