Page Sumary does not include rows with negative values when use pageSummaryFunc = GRIDVIEW::F_SUM

Prerequisites

[x] I have searched for similar issues in both open and closed tickets and cannot find a duplicate.
[x] The issue still exists against the latest master branch of yii2-grid.
[x] This is not an usage question. I confirm having gone through and read the documentation and demos.
[x] This is not a general programming / coding question. (Those should be directed to the webtips Q & A forum).
[x] I have attempted to find the simplest possible steps to reproduce the issue.
[ ] I have included a failing test as a pull request (Optional).

Steps to reproduce the issue

Render GridView with following config (only included those required for sumarization):

echo GridView::widget([

***

'dataProvider' => $dataProvider,
'toolbar' => [],
'hover' => true,
'panel' => [
    'type' => 'info',
    'heading' => 'Detalles',
    'footerOptions' => ['class' => ''],
    'beforeOptions' => ['class' => ''],
    'afterOptions' => ['class' => '']
],
'panelFooterTemplate' => '',
'showPageSummary' => true,
'pageSummaryPosition' => GridView::POS_BOTTOM,
'pageSummaryRowOptions' => [
    'class' => 'kv-page-summary warning',
    'style' => 'text-align: right;',
],
'columns' => [

    ***

    [
        'class' => DataColumn::class,
        'attribute' => 'monto_debe',
        'format' => 'decimal',
        'pageSummary' => true,
        'pageSummaryFunc' => GridView::F_SUM,
        'pageSummaryOptions' => [
            'prepend' => Moneda::findOne(['id' => 1])->simbolo . ' ',
            'append' => '',
        ],
        'contentOptions' => # no matter ~~
    ],
    [
        'class' => DataColumn::class,
        'attribute' => 'monto_haber',
        'format' => 'decimal',
        'pageSummary' => true,
        'pageSummaryFunc' => GridView::F_SUM,
        'pageSummaryOptions' => [
            'prepend' => Moneda::findOne(['id' => 1])->simbolo . ' ',
            'append' => '',
        ],
        'contentOptions' =>  # no matter ~~
    ],

    ***
],
]);

Expected behavior and actual behavior

When I follow those steps, I see the following:

The column DEBE is 14 units more than the column HABER, right?

The database table accessing for those rows is:

The red-arrowed row with a negative value, -14, is not being included by GridView to sumarize rows.

I was expecting something like the following:

Here, I changed at database level the value -14 to 14 so the column DEBE is 28 units greater than the column HABER. The orange text is used to show up the expected correct value.

OBS: The value of the second column, HABER is the desired value to be appearing in both column, for DEBE and for HABER simultaneously.

Environment

No needed

Browsers

[x] Google Chrome
[x] Vivaldi
[x] Opera
[x] Mozilla Firefox
[ ] Internet Explorer
[x] Safari

Operating System

[x] Windows
[x] Mac OS X
[x] Linux
[ ] Mobile

Libraries

***
use kartik\detail\DetailView;
use kartik\grid\DataColumn;
use kartik\grid\GridView;
use yii\data\ArrayDataProvider;
***

jQuery version: - integrated with Yii2, not forced to use custom version --
yii2-grid version: dev-master 1222cdb

kartik-v / yii2-grid

Page Sumary does not include rows with negative values when use pageSummaryFunc = GRIDVIEW::F_SUM #935