I have compiled the tcl program with Tcl8.6 library, i see only the pthread_mutex_unlock and pthread_XXXX function calls. With Tcl8.6 library i didn't see any free() function call while deleting the Tcl Interpreter.
FYI I compiled and ran this program on the same server. I did not do any configuration changes on this server.
Does it proves the problem is with Tcl?