Selecting emoji from dropdown with mouse doesn't work

### Steps to reproduce
1. Go into issue list in some repo
2. Click "New Issue"
3. Type `$`
4. Select the top emoji (`:100:`) from the dropdown with the mouse
### Expected result

Dropdown disappears and the `$` is replaced with a `:100:`
### Actual result

Dropdown disappears but the `$` hasn't been replaced
### Other

OS: Ubuntu 12.04 LTS
Browser: Google Chrome Stable Version 40.0.2214.111 (64-bit)

No files or tests are named. Start by reproducing the mouse selection flow in the issue list's New Issue textarea with the reported emoji dropdown, then trace the dropdown click handling and replacement behavior. Done means selecting :100: with the mouse replaces the typed $ and the dropdown closes.

Written by the indexing model from the issue text.