Is Examine search ignoring certain keywords or my query is wrong?

Question

I am building Examine search in Umbraco and am searching by either keyword or country code or city but I am getting wrong results for some of them.

For example I search for countryCode = IN and startCity = New Delhi

I pass a list of required properties (MUST properties):

List<string> matchProperties =  new List<string> { countryCode = "IN", startCity = "New Delhi" };

But the Examine builds the query as:

SearchIndexType: "content", LuceneQuery: {+(__NodeTypeAlias:product +startCity:"new delhi" -umbracoNaviHide:1) +__IndexType:content}

evidently ignoring countryCode IN value

Same if I search only by country:

List<string> matchProperties =  new List<string> { countryCode = "IN" };

I receive the following query:

SearchIndexType: "content", LuceneQuery: {+(__NodeTypeAlias:product -umbracoNaviHide:1) +__IndexType:content}

Here I am getting wrong results, because the search returns all product nodes instead of the ones containing IN countryCode.

If I look up by a keyword (it uses Or properties so should return products when either of fields contain the keyword) it's included in the query:

SearchIndexType: "content", LuceneQuery: {+(__NodeTypeAlias:product heading:danakil tags:danakil description:danakil -umbracoNaviHide:1) +__IndexType:content}

but it again returns all nodes which is wrong because FOR SURE only a few nodes (up to 20) contain this specific word (case sensitive or not).

But if I search by a fake/ non-word keyword eg. asdadasda:

List<string> matchOrProperties =  new List<string> { keyword = "asdadasda" };

it also gets ignored in the query (same like IN above):

SearchIndexType: "content", LuceneQuery: {+(__NodeTypeAlias:product -umbracoNaviHide:1) +__IndexType:content}

and returns all nodes instead of 0 nodes.

This is how I am building my query:

    protected async Task<List<SearchResult>> SearchCriteriaResultAsync(Examine.Providers.BaseSearchProvider searcher, ISearchCriteria searchCriteria, string contentAliasToMatch, bool excludeHidden, Dictionary<string, string> matchProperties, Dictionary<string, string> matchOrProperties)
    {
        IBooleanOperation query = searchCriteria.NodeTypeAlias(contentAliasToMatch);

        if (matchProperties != null && matchProperties.Any())
        {
            foreach (var item in matchProperties)
            {
                query = query.And().Field(item.Key, item.Value);
            }
        }

        if (matchOrProperties != null && matchOrProperties.Any())
        {
            int counter = 0;
            foreach (var item in matchOrProperties)
            {
                query = query.Or().Field(item.Key, item.Value);
                counter++;
            }
        }

        if(excludeHidden)
        {
            query = query.Not().Field("umbracoNaviHide", "1");
        }

        return await System.Threading.Tasks.Task.Run(() => {
            return searcher.Search(query.Compile()).ToList();
        });
    }

And my indexer and searcher:

    <add name="PublishedProductsIndexer" type="UmbracoExamine.UmbracoContentIndexer, UmbracoExamine"
         supportUnpublished="false"
         supportProtected="true"
         interval="10"
         analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net"/>



    <add name="PublishedProductsSearcher" type="UmbracoExamine.UmbracoExamineSearcher, UmbracoExamine"
         analyzer="Lucene.Net.Analysis.Standard.StandardAnalyzer, Lucene.Net"/>



<IndexSet SetName="PublishedProductsIndexSet" IndexPath="~/App_Data/TEMP/ExamineIndexes/PublishedProducts/" IndexParentId="1049">
    <IndexAttributeFields>
        <add Name="id" />
        <add Name="nodeName" />
        <add Name="updateDate" />
        <add Name="writerName" />
        <add Name="path" />
        <add Name="email" />
        <add Name="nodeTypeAlias" />
        <add Name="parentID" />
    </IndexAttributeFields>
    <IncludeNodeTypes>
        <add Name="product"/>
    </IncludeNodeTypes>
</IndexSet>

Is Examine ignoring certain keywords or my query is wrong? If wrong how should I fix it?

I ma using umbraco 7.6 if this matters.