Unagi Compositing Manager

When restarting Awesome (via awesome.restart()), Unagi exits with the following message:

opacity.c:255: opacity_event_handle_property_notify: Zusicherung »opacity_window« nicht erfüllt.

(Which roughly translates to "opacity.c:255: opacity_event_handle_property_notify: Assertion "opacity_window" failed")

GDB produces the following backtrace:

(gdb) run -c .config/unagi/unagi.conf
Starting program: /usr/local/bin/unagi -c .config/unagi/unagi.conf
unagi: opacity.c:255: opacity_event_handle_property_notify: Zusicherung »opacity_window« nicht erfüllt.

Program received signal SIGABRT, Aborted.
0xffffe424 in __kernel_vsyscall ()
(gdb) bt
#0  0xffffe424 in __kernel_vsyscall ()
#1  0xb7e3e421 in raise () from /lib/libc.so.6
#2  0xb7e3fb62 in abort () from /lib/libc.so.6
#3  0xb7e375c8 in __assert_fail () from /lib/libc.so.6
#4  0xb7fdeb7a in opacity_event_handle_property_notify (event=0x805b7a0, window=0x805b3b0) at opacity.c:255
#5  0x0804b8fb in event_handle_property_notify (data=0x0, c=0x8053038, event=0x805b7a0) at event.c:624
#6  0xb7f8cf35 in xcb_event_handle (evenths=0x80513f0, event=0x805b7a0) at event.c:77
#7  0xb7f8cfac in xcb_event_poll_for_event_loop (evenths=0x80513f0) at event.c:98
#8  0x0804e410 in main (argc=3, argv=0xbffff054) at unagi.c:383