The issue might be specific to testwiki setup, otherwise the issue is a regression.
Note:
1. Without new filters I did not see any problems with articles' titles display in test wiki.
2. I did not see any problems with articles' titles display in wmf.10
1. Enable RC filters and click on Random page option on the left side navigation. Keep going through random articles until you see an article with two (or more) words in the title.
2. Click on the Related changes - the article title will be displayed with white spaces indicated with underscores.
{F11211087}
{F11211090}
Since testwiki has a variety of article titles in different languages - Related changes will display several cases of url-encoded titles in the text box:
{F11211009}
{F11211005}
One of the most mangled titles:
{F11211080}
{F11211084}