I'm having a problem with Valgrind telling me I have some memory possible lost:

==23205== 544 bytes in 2 blocks are possibly lost in loss record 156 of 265
==23205==    at 0x6022879: calloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==23205==    by 0x540E209: allocate_dtv (in /lib/ld-2.12.1.so)
==23205==    by 0x540E91D: _dl_allocate_tls (in /lib/ld-2.12.1.so)
==23205==    by 0x623068D: pthread_create@@GLIBC_2.2.5 (in /lib/libpthread-2.12.1.so)
==23205==    by 0x758D66: MTPCreateThreadPool (MTP.c:290)
==23205==    by 0x405787: main (MServer.c:317)

The code that creates these threads (MTPCreateThreadPool) basically gets an index into a block of waiting pthread_t slots, and creates a thread with that. TI becomes a pointer to a struct that has a thread index and a pthread_t. (simplified/sanitized):

for (tindex = 0; tindex < NumThreads; tindex++)
  {
  int rc;
  TI = &TP->ThreadInfo[tindex];
  TI->ThreadID = tindex;

  rc = pthread_create(&TI->ThreadHandle,NULL,MTPHandleRequestsLoop,TI);
  /* check for non-success that I've omitted */
  pthread_detach(&TI->ThreadHandle);
  }

Then we have a function MTPDestroyThreadPool that loops through all the threads we created and cancels them (since the MTPHandleRequestsLoop doesn't exit).

for (tindex = 0; tindex < NumThreads; tindex++)
  {
  pthread_cancel(TP->ThreadInfo[tindex].ThreadHandle);
  }

I've read elsewhere (including other questions here on SO) that detaching a thread explicitly would prevent this possibly lost error, but it clearly isn't. Any thoughts?