Multilist field Index issue When Index only selected field

Problem:

We added a new multi-list field in Sitecore 9 Update 2, (vanilla instance) on the Sample Item and populated it with some content items.
We Added new multi-list field to include the fields section in the index configuration file as: 
            xxxxxxx  

also set
false
under documentOptions node in Sitecore 9 update 2

We rebuild the sitecore_master_index and we queried the index in Solr. We noticed that the field is stored in the index as a string in the format of an array of IDS. - this is not what we expected."multilistitem_t_en":["{Guid1}|{Guid2}"],

If we turn true and rebuild the index we see the field in the index as a string in the format of a list og GUIDs which is what we expect to be the default behaviour."multilistitem_sm":["23442343231423423234abcdbded", "bced4423433231423423234abcdbded"],We don't want to change indexAllFields to true though due to performance issues.

Solution:

Due to this issue, we had to postpone the release by a day and out team needs to change all our multi-list fields code to computed fields. After some time Sitecore has provided a fix

 https://github.com/sitecoresupport/Sitecore.Support.252532/releases.

Happy sitecoring........