Using Parent tag in search form doesn't pull contacts marked with child tag in search form result

Reproduction steps

Steps to replicate:

1. Create a parent tag A and child tag A1
2. Create/update contact and tag with A1
3. Go to 'Find Contacts' or 'Find Contributions' and search by Tag - A

Current behaviour

1. In 'Find Contact' result, it doesn't show contact which is tagged with child tag A1
2. In 'Find Contributions' result, it doesn't pull contribution(s) of contact tagged with child tag A1 

Expected behaviour

Searching using a parent tag should automatically include the contacts which are in parent tag A and in its n child tag(s) - An. In this use-case it should show contact tagged with child A1 tag.

Comments

ping @JoeMurray @eileen @seamuslee @lcdweb