At work I'm getting an assert here:

static void update_stack_stats(SSizeT stack_szB_delta)
{
   if (stack_szB_delta < 0) tl_assert(stacks_szB >= -stack_szB_delta);
   stacks_szB += stack_szB_delta;

   update_alloc_stats(stack_szB_delta);
}

I think that means that is asserting that the stack size does not go negative.

I'm debugging it in gdb to try to see where what is causing it in the guest.