Ok, so part of the problem was that I still had the following workaround (to maximize the height of ChildGridViewTemplates upon expansion) enabled: http://www.telerik.com/community/forums/winforms/gridview/child-grid-vertical-size.aspx
This workaround is no longer applicable in Q3 2009 (or at least it should be no longer applicable ;P).
However, the following issues still apply that make ChildGridViewTemplates' Heights either too short OR
It's not auto -shrinking / -expanding a ChildGridViewTemplate's Height when:
- Rows are grouped / un-grouped.
- Groups are collapsed / expanded.
- Switching between sibling sub-tables.