Using lain at 41ccab3 with my fork of awesome-copycats and it seems that of the terminals I have installed, xterm toggles with Mod + z but termite does not. No errors, it just simply does not appear. My fork, sboysel/awesome-copycats@67632cc, has some very minor differences from lcpz/awesome-copycats@0d80ca0 that I don't think are related to this issue.

[sam@archbook ~ 08:22:18]$ uname -a
Linux archbook 4.6.3-1-ARCH #1 SMP PREEMPT Fri Jun 24 21:19:13 CEST 2016 x86_64 GNU/Linux
[sam@archbook ~ 08:22:13]$ termite --version
termite v11

Let me know if I should open the issue in awesome-copycats or if the issue is beyond the scope of what you're willing to support.