To reproduce the bellow issue:

• Sort the issues by parent task
• Resize the screen until the Assignee goes also on two lines
• Have at least on parent issue with a subject on two lines
• Have a child issue with a short subject.

!issue_list_before.png!

The attached patch fixes this.

!issue_list_after.png!

I chose to change from top to middle for all table.list td because I don't see any side effect of this change. If it's not ok, i can update the patch to target only the table.list.issues td