Board scope failing with certain characters

Summary

Issue boards with a milestone filter fail whenever the milestone title includes certain special characters.

Steps to reproduce

1. Create a milestone with "+" on the title, such as "support C++11"
2. Create a board with a Board scope based on the milestone.
3. The URL shows: /boards?milestone_title=support C%2B%2B11&=

What is the current bug behavior?

The milestone issues are not appearing due to the character encoding.

What is the expected correct behavior?

Show the milestone issues on the board.