Weight of epic is updated unexpectedly when child epic is expanded

Steps to Reproduce

1. Navigate to an epic (such as &2864, to use an arbitrary example)
2. Notice collective weight at top of epic/issue list (let's say it's 242)
3. Click chevron of a child epic to expand it (let's say &5079 (closed) "🏗 Epic Boards - MVC 3 - Final polish and parity for final release")
4. Expected: Collective weight (total weight of parent epic) should not change
5. Actual: Collective weight gets updated to equal the weight of the expanded epic (from 242 down to 22, given the weight of the expanded child epic is 22)
6. Notice that clicking the chevron on another child epic to expand it will update the weight again, to match the weight of the second expanded epic
7. Notice that collapsing a child epic does not cause the collective weight to update (it never goes back up)
8. Notice that expanding a child epic that was previously expanded does not cause the collective weight to update (it always stays at the weight of the most recently, newly expanded child epic)