Hello Darren,
After replying you on email I also post our response here for future users. We are aware of these glitches on this HTML-based theme but unfortunately there are out of our reach to fix.
The HTML host control is rendered using the native Microsoft WebBrowser object within an ActiveX host window. Since this control uses the same core engine as the Microsoft Internet Explorer browser installed on the system, it leverages all its core functionality, like: HTML rendering engine, JavaScript VM, plug-ins, etc.
We simply emulate HTML content by using the
IWebBrowser2 API offered by Microsoft:
This theme was intended to be used for the freedom of HTML-based customizations. If you're not using it to considerably customize the layout, The only workaround I can think of is to try using any other theme.
All the best,
Daniel