icalarray_append(builtin_timezones, ...) is called. This can cause
icalarray_expand() to be called, moving the entire builtin_timezones
array and thus invalidating any previous pointers into the array.
Additional notes here, including backtraces of the crash and a valgrind
log catching the access to freed memory red handed:
"Your valgrind log exactly points out that its fundamentaly broken and needs to be fixed." - from Wilfried Goesgens in https://sourceforge.net/mailarchive/message.php?msg_id=29079904