Milestone time tracking does not consider time estimated and spend under linked Merge Requests

Summary

Milestone time tracking does not consider time estimated and spend under linked Merge Requests

Steps to reproduce

• Create Milestone
• Create new Merge Request and link it with Milestone
• Make "/spend X" at Merge Request

What is the current bug behavior?

Milestone's "Total issue time spent" statistics does not changed

What is the expected correct behavior?

Milestone's "Total issue time spent" statistics changed considering linked Merge Requests time tracking

Results of GitLab environment info

GitLab Community Edition 10.4.2 b1c501c9