Bug, Edit datatable column with colapsed columnGroup

Webix JS
1

I get an error when i edit a column in a datatable with column groups, when one of the groups is collapsed. If all groups a not collapsed everything works fine.
Can you please check my code: http://webix.com/snippet/f790d540

Doubleclick a month column, change the number and press enter → everything fine.
Do the same when one column group is collapsed → error

2

Caused by Math using.

When you are closing group of columns, it effectively remove the hidden columns from the DataTable but formulas that refer to those columns are still active.

We will try to resolve the issue in the next update.