I have made some progress and that progress has allowed me to continue with my solution. However its not a fix for the original issue.
It turns out that the CustomForm module has two POST controller actions, one to save (submit.Save) and one to publish (submit.Publish). By using the publish action I was able to correctly publish new content and that content appears in the query preview.
Further it turns out that the save (submit.Save) action will save a draft if the content type is draftable but will publish the content if the content type is NOT draftable. Hence I am able to work around my issue by making my content type non draftable.
This is a work around for my problem but does not answer the original question.
I have also looked into the original problem where apparently published content is not returned from the query. It appears to be to do with the join to FieldIndexPartRecord in the following HQL which returns no results when the content has been published via
select distinct civ.Id as Id
from Orchard.ContentManagement.Records.ContentItemVersionRecord as civ
join civ.ContentItemRecord as ci
join ci.ContentType as ct
join ci.FieldIndexPartRecord as fieldIndexPartRecord
join fieldIndexPartRecord.StringFieldIndexRecords as InsuranceProposalProposerName
where (ct.Name in ('InsuranceProposal')) AND (InsuranceProposalProposerName.PropertyName = 'InsuranceProposal.ProposerName.' and InsuranceProposalProposerName.Value like '%k%' ) AND (civ.Published = True)
order by civ.Id