After making some tests with your latest version 2.31.06, I finaly understand why noExtenInLabel doesnt work for certain and work for others.
If you configure your users/buttonfile in the "general" context of /usr/local/fop2/fop2.cfg and call your fop2 : http://your_server/fop2, it work fine
BUT...
If you configure your fop2 to be multi-tennant and configure your users/buttonfile in a custom context, exemple :
[blablabla]
user=blablabla1000:5555:all
buttonfile=buttons_blablabla.cfg
then call you fop2 with the custom context : http://your_server/fop2/?context=blablabla
The noExtenInLabel doesnt work anymore, even if your activate it in the admin menu or in the presence.js file.