I have three address books and tons of email: One SoGO address book I only rarely use, my Personal Contacts that I often use and some linkedin import that is there in case I don't have the person in the other two. Baloo indexed all my email. Now I want to write a new message. 
In KMail, I click on new message. In the to: field I start typing the last name. After 4 letters, a long list of suggestions is shown. (Works really quickly now). The list is organized according to the sources the suggestion comes from. 
Often, I know positively that there is a contact in my personal contacts. If I start to type the last name, sometimes only addresses from SoGO are shown plus a long list from "other sources" that Baloo had recorded from the indexed emails (With all the variations of the email address name that was ever used in the emails I received from others). So completion works, but not as expected. 

Reproducible: Always

Steps to Reproduce:
1. create new email
2. type in last name of one of your contacts 
3. enjoy a long unordered list of all iterations of that email known to the system
Actual Results:  
Precision is fine as I have only rarely/none false positives. Recall is low as results are missing. I know I have a contact in my personal contacts and it isn't shown. Instead, only the result from the SoGO address book is shown and a long list of matches generated from harvesting my incoming email

Expected Results:  
Better recall: At least the addresses from the local address books should be found reliably
Better ordering: The email address is a unique ID, thus very easy to sanitize in an IT system. So the email should be only shown once from every source. It may make sense to let the user expand the list with a [more ...] to see the full list of matches

The address books should be shown in order: Local first and then remote and then what was harvested from the incoming email.