Custom filtering combined with built-in search and filtering

Good morning,
 
I’m attempting to implement a ASP.NET MVC grid with custom filter functionality that’s integrated with my grid filters. However, I’m struggling with filter values getting overwritten when performing search filter functionality.
 
In my grid I have inline grid row filtering:
                          .Filterable(filterable => filterable
                               .Extra(false)
                              .Operators(operators => operators
                                  .ForString(str => str.Clear()
                                      .IsEqualTo("Is equal to")
                                      .IsNotEqualTo("Is not equal to")
                                      .StartsWith("Starts with")
                                      .Contains("Contains")
                                      .DoesNotContain("Does not contain")
                                      .EndsWith("Ends with")
                                      .IsNull("Is null")
                                      .IsNotNull("Is not null")
                                      .IsEmpty("Is empty")
                                      .IsNotEmpty("Is not empty")
                               ))
                           )
I also make use of inline grid search as filtering. This search functionality is defined in my grid toolbar:
                       toolbar.Search();
Lastly, for my mentioned custom filter functionality, I have defined two multiselects in my grid toolbar. These multiselects make use of a JavaScript onchange event that gets fired upon changing the multiselect value. This JavaScript function calls grid.dataSource.filter() to apply the filtering and then automatically call the grid read event. The set-up for this code is comparable to the example for the grid toolbar template: https://demos.telerik.com/aspnet-mvc/grid/toolbar-template
To retrieve my results, I make use of a datasource with .webApi() configuration, making use of a controller method that gets called with my read event. This controller method contains a DataSourceRequest that contains the set filters. The problem I’m facing is that when I input text into my search filter, that the set multiselects filters get overwritten.
Is there a way I can perform search and column filter functionality without it overwriting my multiselect filters?
ASP.NET MVC Grid Toolbar Template Demo | Telerik UI for ASP.NET MVC
This Telerik ASP.NET MVC Grid example shows how you can add custom toolbars to the grid and create toolbar templates.

https://demos.telerik.com/aspnet-mvc/grid/toolbar-template