I found this from latest git version.

In file perf/cairo-perf-graph-files.c:322: 
Variable id is allocated with:
char *id = g_malloc (len + 1);

And later released:
free (id);

"It's important to match g_malloc() with g_free(), plain malloc() with free(), and (if you're using C++) new with delete and new[] with delete[]. Otherwise bad things can happen, since these allocators may use different memory pools (and new/delete call constructors and destructors)."
http://library.gnome.org/devel/glib/stable/glib-Memory-Allocation.html

ps. The version drop down list does not have "git" or similar option for bugs found from the very latest source files. 

This bug was found using cppcheck: http://cppcheck.wiki.sourceforge.net/