Dimension Security Issues with Excel 2007 and SSAS 2005 Parent-Child Hierarchies

I've seen and read a lot of different posts and blog entries related to Excel 2007 and SSAS 2005 issues. Mostly things that don't work as planned with regards to displaying and using calculated members, incorrect query results given Excel's subcube-based filtering and its interaction with default members, etc. But here's one that I don't think I've run across yet that actually causes an error to occur while browsing a cube...