The reason that "nothing happens" is because of double Auto for grid rows' height - if you set all rows height with Auto for a vertically stretched grid then the last height will be actually treated as initialized with the asterisk instead.
About the code-behind: there is no need to collapse the expander content. The expander will collapse and visualize it automatically.
Attached you can find an example having your code multiplied four times in order to demonstrate different settings for grid rows height. Please note the following:
- some margins and backgrounds are changed to emphasis the layout;
- at the very top row there is information about the height of grid-rows;
- in the third example (column) there is an additional MinHeight & MaxHeight for the first grid row;
- Grid's ShowGridLines is set to True to visualize the layout.
Please give a try and let me know if additional assistance is needed.
the Telerik team