Qemu crashes on Mac (emulation of  x86_64)

I used qemu on MAC OS X Yosemite with the latest qemu version (from git, 6. august 2015, QEMU emulator version 2.3.94, Copyright (c) 2003-2008 Fabrice Bellard)

I configured it with "./configure --enable-vde".

Sometimes when starting an openwrt instance, the following error occurrs in the qemu monitor:

(qemu) qemu:qemu_cpu_kick_thread: No such process

I started qemu this way:

qemu-system-x86_64 -m 128 -serial unix:/tmp/qemu_1.sock,server,nowait -nographic -net nic,macaddr=aa:aa:aa:aa:00:01 -net vde,sock=/tmp/vde_switch_1 -watchdog-action poweroff openwrt-x86-generic-combined-ext4.img

The same works on Linux (Ubuntu 14.04, qemu-2.4.0-rc3).