This is an issue that results from directly following the steps to reproduce EZP-26707:

1. Install Solr Bundle (https://doc.ez.no/display/DEVELOPER/Solr+Bundle), make sure Solr service is running;

2. Configure autoSoftCommit to 100, on:
solr/collection1/conf/solrconfig.xml

3. Create a new Content Type that contains a searchable field:
Name: MyCT
Identifier: myct
fields:
Field Type: Text Line
Name: Name
Identifier: name
Searchable: checked

4. Create a new content for that class, named "MyContent", and publish;

5. Go to Search, and search for "MyContent", and verify that it is found;

6. Edit the Content Type "MyCT" and uncheck the "Searchable" option for the searchable field "Name", and publish;

7. Search again for "MyCT". It should no longer be found, but it is (even after the fix for EZP-26707);
This means the updated changes on Content Type were not automatically indexed on Solr;
However, manually reindexing with Solr will make the Search for the content no longer return results, which renders the changes to the Content Type update properly indexed on Solr.
According to petar.spanja@ez.no's comment on EZP-26707:

OK, I forgot about this detail – the reason for this behavior is we don't reindex Content when ContentType changes.
You can file this but I think it should go as an improvement, as we need several missing things to handle it properly:
synchronous search/filtering to find all Content that needs to be reindexed
delayed indexing when large amount of Content is affected
That means at the moment full reindex is required when ContentType changes.

this is meant to be handled as an improvement with several tasks to handle, hence this jira having been created.