This was corrected in s2Member v110926.
This bug may have impacted *new* installations of s2Member v110912 - v110915, and even after upgrading to s2Member v110926+, the bug may still appear to exist, because the options are already configured. The solution in these cases, is to change the values manually in the s2Member config panels. %first_name% needs to become %%first_name%%, etc.
This bug does NOT affect anyone that upgraded s2Member from a version prior to v110912.
(s2Member/s2Member Pro) Bug fix. A bug first introduced in s2Member v110912 was causing problems with s2Member's default email customization templates. Double percent signs %% for Replacement Codes were being reduced by s2Member's internationalization routines, to just single percent signs %, thereby nullifying them as valid Replacement Codes. Fixed in this release. If you installed s2Member and/or s2Member Pro v110912 - v110915 on a clean installation of WordPress®, it would be a good idea to have a quick look at your email customizations with s2Member, just to make sure your Replacement Codes have double percent signs around them ( for example, this is valid: %%registration_url%%, and this is NOT valid: %registration_url% ).