No, this is some kind of error in the column definition. If you change the vb:column (on line 895 in gui.lua) into vb:row, you will see those buttons.
But you have to add some extra stuff into the main.lua as well to get the errors out…
Ah hell, just download the correctly updated tool here (2.7 download version added):
http://tools.renoise.com/tools/zynzilla
Thanks vV.
vV to the rescue! 
Cool, thank you.
I love this tool so much and I really miss it in 2.8. wink wink
didn’t this one stop working in 2.7 already?
vV fixed it so it worked in 2.7…
Here’s a new version of ZynZilla which is based off of @martblek’s recent update (see this for reference).
This version allows to pass key presses through, as requested by @slujr in this post. I also added a quick change of my own: newly created samples are automatically set to “loop forward” to take advantage of @slujr’s update suggestion.
com.noisebeuter.ZynZilla.xrnx (11.2 KB)
THANK YOU!!! 
this is sweet!
Updated version that addresses a bug with the “wave” wave type as mentioned here.
com.noisebeuter.ZynZilla.xrnx (11.3 KB)
You rock! 
Wait, this is crazy! you can now insert any instrument sample as the zynzilla wave 
this opens up a lot of interesting territory…
this is beyond a bug fix, it’s a whole other level of functionality
KUDOS
Ha, well it is technically a bug fix that made the existing wave functionality usable.
But still! Awesome
Had a bug playing with the latest version;
"‘C:\Users\pluge\AppData\Roaming\Renoise\V3.4.2\Scripts\Tools\com.noisebeuter.ZynZilla.xrnx\main.lua’ failed in one of its notifiers.
Please contact the author (Marco Süß | noisebeuter (redacted) + Fabio Napodano | It-Alien (redacted) for assistance…
main.lua:350: attempt to index local ‘harmonics’ (a nil value)
stack traceback:
main.lua:350: in function ‘prepare_harmonics_and_phase_shifts’
main.lua:424: in function ‘process_data’
main.lua:572: in function ‘generate’
.\gui.lua:549: in function <.\gui.lua:534>"
Just clicking randomly in the gui between tabs.
Now when I close it and re-open the tool;
“main.lua:350: attempt to index local ‘harmonics’ (a nil value)
stack traceback:
main.lua:350: in function ‘prepare_harmonics_and_phase_shifts’
main.lua:424: in function ‘process_data’
main.lua:572: in function ‘generate’
.\gui.lua:644: in function <.\gui.lua:642>
[C]: ?
[C]: in function ‘__newindex’
[string “do…”]:22: in function <[string “do…”]:9>
.\gui.lua:166: in function ‘change_wave’
.\gui.lua:918: in function ‘show_dialog’
main.lua:148: in function main.lua:148”
Clicking away the above automatically a Renoise script termination window, asking if you want to stop processing, clicking yes gives;
“main.lua:532: Script execution terminated by user.
stack traceback:
[string “do…”]:37: in function <[string “do…”]:35>
main.lua:532: in function ‘generate’
.\gui.lua:662: in function <.\gui.lua:660>
[C]: ?
[C]: in function ‘__newindex’
[string “do…”]:22: in function <[string “do…”]:9>
.\gui.lua:127: in function ‘change_tab’
.\gui.lua:919: in function ‘show_dialog’
main.lua:148: in function main.lua:148”
it keeps popping up the termination window and above error message;
"‘C:\Users\pluge\AppData\Roaming\Renoise\V3.4.2\Scripts\Tools\com.noisebeuter.ZynZilla.xrnx\main.lua’ may be busy or may have stopped responding.
You can stop the script now, in order to avoid freezing the whole program or continue waiting for it to complete.
Terminate Script?"
I did see this yesterday, and I thought I had reproducible steps to try to figure out this issue today, but now I can’t reproduce it. I swore it had something to do with using the “Wave” wave type and switching tabs. Do you remember the particular scenario when this happened (how many operators where active, which kind, etc)? I’ll look into this and the other one you reported anyway.
I’ve also noticed that the tool doesn’t handle phase shift values of less than 1 gracefully for “Wave” wave types.
Not sure exactly, wil try and see if I can replicate.
I haven’t been able to get any of the bugs reported by @Jonas, so I don’t know what to look for, unfortunately. When I switch tabs, the tool doesn’t crash, so I am not sure what the condition for the crash could be. Hopefully if they appear again, there will be reproducible steps to follow.
I did make an update to the “Wave” wave type’s phase shift control. It was originally crashing the tool at negative phase shift values, but now it works as intended, I think.
com.noisebeuter.ZynZilla.xrnx (11.4 KB)