When endless scrolling and grouping is enabled on the KendoUI grid, collapsing large groups causes the grid to load ALL the hidden detail rows into the DOM.
This takes a very long time for the grid to do, as well it violates the whole point of a paging system. (ie I only want you to load X records at a time). Afterwards the performance of entire website (including the grid) will be very poor since potentially thousands of rows have been loaded into the grid and then immediately hidden. Additionally, these rows do not add any value to the user, since they are all hidden anyways.
When a category is collapsed, the grid should NOT add any new rows for that category to the DOM.
I have included a sample that demonstrates the performance issues.