This is not a bug. Checking for the existance of child rows can be an expensive operation. So the tree doesn't check until the first time you attempt to expand the parent node. That is the default, but you can change this behavior using the ExpansionIndicator property, which is on the Override, I beleive.
I guess there might ge a bug with the UltraTree 7.3. I found a work around. I iterate though the node and if it does not have children i expand. That make the expand icon to disappear.