But there is a problem. I test in your demo, For any row, when the expander is in expanded state, and i try to click the column title, the grid sort data, and the expander panel just disappears and will not be there anymore.
Sorry for my english, you can test your demo:
1. click a row, to expand the expander panel
2. click column title to sort
3. click same row, but the expander panel never appear
It happens to me too. Adding the fix, when sorting, the expanded panel disappears, although we can later collapse and expand and it appears again. But it would be great if this wouldn't disappear.