std::string memory leak?

[Carlos Martinez]

Hi all:

I have a possible memory leak.
I use rational's purify to detect memory leaks, and it indicates a
memory leak in a temporary of std::string.

I have read somewhere that some memory leaks aren't memory leaks at
all. It seams it could be the memory pool used by the stl.
I have test with and without GLIBCPP_FORCE_NEW environment variable
enabled, and in both cases there is the memory leak.
I assume it's a memory leak, because without purify, processes grows
up in memory usage indefinitely  and because if I change std::string
for my own very, very basic implementation of string, it disappears
(no memory growth nor memory leak indication by purify)

Thanks in advance