Why can't tags be found with full text search ?
It sounds a bit strange to me that there is a separate search for tags and for text search. Imagine you have thousands of documents with each a couple of tags attached to it: how would you be able to find the right tag you want to use to search for a certain document ?
This is indeed a missing feature: the names of the tags could be aggregated in the fulltext index field of the tagged documents. I opened a jira issue to track this feature request:
Please feel free to register on jira and vote for this issue to increase it's priority. Alternatively please feel free to submit a pull request on github :)