Loading a XAML file that contains an iframe pointing to another XAML file causes a crash in the WPF rendering pipeline.

<!-- 02.html -->
<iframe src="03.xaml"></iframe>

The chain is: 01.xaml (XAML Frame) → 02.html (HTML with iframe) → 03.xaml (nested XAML). The nested XAML-in-XAML rendering through the HTML intermediary was the triggering condition.

Found during my years at Microsoft (2006–2014). These bugs were patched long ago — shared here as a historical record for learning purposes.