The constructor for TranscodeToStr calls TranscodeToStr::transcode(). That method allocates memory for fString, but it is possible for an exception to occur shortly thereafter; it might be thrown directly by transcode(), or by the transcoder method call trans->transcodeTo(). Since we are still in the constructor, TranscodeToStr's destructor will not be called during the stack unwind to clean up (see http://www.parashift.com/c++-faq-lite/exceptions.html#faq-17.10 ). Therefore, we have to explicitly make sure fString will be deallocated. Since the current code doesn't do that, it leaks memory. TranscodeFromStr is in the same situation.
I have a simple patch that I expect to post later tonight.