two instances of malloc.h: is it normal?

Scanning through the /usr/include I’ve noticed that there are two
DIFFERENT files with the same name there:

  1. /usr/include/malloc.h 6,417 Jul-17-1996 17:48 (it’s the link to

  2. /usr/include/sys/malloc.h 7,424 Mar-09-2000 20:34 (that one is the link
    to /usr/tcptk/5.0/usr/include/sys/

Seems this happened because of updating TCP/IP stack to v5.0A
Is this situation normal?
If not - what to do?