Group method not work if filter value

Hello,
Please see for review.
https://webix.com/snippet/b2f460e6

  1. Do grouping
  2. Set a filter value
  3. Do regroup

Grouping is a client-side feature that works with the data available in the datatable right now.
Applied filtering excludes items from the current order and therefore will interrupt it, so the best option is to reset filters before grouping via datatable.filter() without parameters.