I thought I would post this here since it's the only thread I've found about <% sprintf(...) %>. Hopefully the info will be helpful to someone that knows more than I do.
<% sprintf(...) %> has been showing up in my CMS admin since last week when I updated my copy of XAMPP from 1.7.1 to 1.7.3. For me at least the problem seems to be connected with what versions of server software are running since I can install Silverstripe on clean installs of XAMPP 1.7.1 and WAMPServer 2.0i and have everything show up correctly. (XAMPP 1.7.3 runs Apache2.2.14, PHP5.3.1, and mySQL5.1.41 while v1.7.1 and WAMPServer both run slightly older versions of each.)
WAMPServer is supposed to support easy install of and swapping between different versions of Apache, PHP, MYSQL. I tried to test my theory and replicate the problem by using that feature but for some reason WAMPServer keeps hanging up on something when it restarts after switching to PHP 5.3.1
Also the sprintf strings show up in installs of different versions of SS but the correct text gets rendered on the pair of remote servers I have ss installed on.