I believe this has to do with the WPF WebBrowser control defaulting to IE7 regardless of what version of IE is installed locally.
Apparently there are two solutions to resolve this.
One is to add a registry value in HKCU\Sofware\Microsoft\Internet Explorer\Main\FEATURE_BROWSER_EMULATION\
Add a new DWORD(32-bit) named InteractionScripter.NET.exe with the desired value.
See this link for information: MSDN
You may be also able to add
I have quickly verified that each of these work by creating a
element with rounded corners. Before making any of these changes, the corners were not rounded. I then modified the registry, and reloaded the page within Interaction Scripter.NET and observed the corners were then round. Next I deleted my new registry value, and inserted the tag into the head of my HTML document, deleted cache, reloaded the page, and observed the corners were still rounded.