I'm pretty sure this belongs to GtkHtml, since many similar issues reported in the past on the Evolution bugzilla were pointed over here. Please correct me if I am wrong. 

I dug through code and changelogs for a good 4 hours today, but was quickly lost and frustrated. I'm pretty sure someone here knows exactly what happened recently.

Running updated Fedora Core 13
gtkhtml2-2.11.1-7.fc13.i686
evolution-2.30.2-1.fc13.i686

After a recent gtkhtml / evolution update, links which encapsulate another link are no longer functioning when clicked or right-click "Open Link in Browser" because the encapsulated link is unescaped before being passed to the browser.

Workaround is to right-click "Copy Link Location" and paste in browser.

Easily duplicated by copying the link from a Google "cached" page and send it to yourself as a link in an HTML email.

http://www.google.com/url?sa=t&source=web&cd=1&ved=0CCQQIDAA&url=http%3A%2F%2Fwebcache.googleusercontent.com%2Fsearch%3Fq%3Dcache%3AulbHQR-5i7cJ%3Awww.gnome.org%2F%2Bgnome%26cd%3D1%26hl%3Den%26ct%3Dclnk%26gl%3Dus&ei=6eVFTCuOkp8H6d-E_gM&usg=AFQjCNFCkBrmoakeGg9IU6W-2VecSxFX9g

The above link include a parameter named "url" which contains an escaped URL which, including it's escaped parameters, to be passed onto the base URL.
  
The value of the 'url' parameter is unescaped before being passed to the browser, thus breaking the parameters the encapsulated URL is expecting to have passed.

Per strace, this is the command issued:
[pid 18577] execve("/opt/google/chrome/google-chrome", 
["/opt/google/chrome/google-chrome", "--new-window", "http://www.google.com/url?sa=t&source=web&cd=1&ved=0CCQQIDAA&url=http://webcache.googleusercontent.com/search?q=cache:ulbHQR-5i7cJ:www.gnome.org/+gnome&cd=1&hl=en&ct=clnk&gl=us&ei=6eVFTCuOkp8H6d-E_gM&usg=AFQjCNFCkBrmoakeGg9IU6W-2VecSxFX9g"], [/* 44 vars */] <unfinished ...>

Notice the original 'url' parameter only contains the www.googleusercontent.com URL, it's parameters are no longer escaped and now part of the base URL 

Google, and many other sites which do this, returns a error/redirect notice not knowing what to do.