CiviMail un-encodes links encoded with php's urlencode, crashes Google forms

Some characters passed on the right of a URL should be encoded, which is why php has a urlencode function.

Problem is, some characters (such as + and %) that are encoded using php's urlencode come out of CiviMail unencoded.

Unencoded % characters crash google forms.

The + is less problematic, it is just interpreted as a space.

See:

http://forum.civicrm.org/index.php/topic,35489.0.html

We have tried sending encoded characters using other mail clients without problem – we have not discovered another mail client with this problem.

We are on CiviCRM 4.1.5