After an initial test, I can find the issue as you have mentioned, we need to investigate the issue. But, even when I opened your Excel file into MS Excel 2007, I also found errors and MS Excel finally repaired the file for display into it.
I have logged a ticket with an id: CELLSNET-40115. We will look into it soon.
For Grouping feature, it is a new and complex feature, we need to customize it accordingly. Currently we will fix it soon.
For the Excel file you submitted to us, when double clicking the rows, there are some errors occurred, We have fixed it and we will soon provide you a fixed version for it here.