Grid grouping issue with DateTime fields

[Shum_Inc]

I have problem with grid rows groupping in 4.2.0 beta.
Store config contains "groupField: 'DateCreate'" where DateCreate is DateTime field with empty time, like this:
Date {Sun Feb 17 2013 00:00:00 GMT+0600 (Ekaterinburg Standard Time)}
and for rows with identically date creating separate groups (with same names).
Another bug - getGroupString working strange. If I assign to store getGroupString function:

getGroupString: function (instance) {
return 'A';
}

- anyway creating multiple groups (instead one "A").
In 4.1.3 all working fine (but with a little visual bug with column resize + grouping - column header width != column width after manual resize).

[Shum_Inc]

UPD: In ext-4.2.0.489-beta all groups creating rights, however getGroupString still not pass to groupHeaderTpl.

[evant]

Not really sure what you mean by:

getGroupString still not pass to groupHeaderTpl.

Can you provide more detail?

[Shum_Inc]

If Store has method:

getGroupString: function (instance) {
  return 'A';
}

and groupField property set to DateTime field - then in 4.1.3 will created one group with name/value "A". Same code in 4.2.0 beta will create one group (that right) but name/value not "A" but original item value.