Hang in embedded libchicken

Dear mailing list,

the following issue has occurred when embedding CHICKEN 5.4.0 in a
multithreaded C program. I have reproduced the issue on macOS and
NetBSD 10. Either I am doing something wrong or this is a bug.

The program I am embedding just returns the squared input.

    ;; x.scm
    (import (chicken platform) (chicken foreign))
    
    (define-external (bar (int i)) int
        (* i i))
    
    (return-to-host)

The C program starts one extra thread and then both threads 
call the exported function bar. To ensure no concurrency issues
occur, I have protected the calls to bar with a pthread mutex.
    
    // y.c
    #include <chicken.h>
    #include <pthread.h>
    #include <stdio.h>
    #include <unistd.h>
    
    extern int bar(int);
    
    static pthread_mutex_t m = PTHREAD_MUTEX_INITIALIZER;
    
    static int call(void) {
        pthread_mutex_lock(&m);
        int r = bar(1);
        pthread_mutex_unlock(&m);
        return r;
    }
    
    static void *run(void *_) {
        printf("value: %d\n", call());
        sleep(1);
        printf("value: %d\n", call());
        return 0;
    }
    
    int main(void) {
        CHICKEN_run(C_toplevel);
        pthread_t t;
        pthread_create(&t, 0, run, 0);
        run(0);
        pthread_join(t, 0);
        return 0;
    }
    
To build and run the test case, I used:

    csc -e -o test x.scm y.c
    ./test

From CHICKEN's documentation, I had the impression that this 
interface usage should be supported. Am I doing something silly?

Can anybody reproduce this issue on other systems?

Last comment: I have started this with gdb and one thread does
not leave C_save_and_reclaim, IIRC. I keeps calling some
mark_* and C_reclaim functions.  My libchicken does not have
symbols, so I couldn't look in more details what is happening,
but it looks like the thread never leaves the function. That
only happens if I call the interface with two or more threads.

-Diogo