I don't think this is a Bukkit problem. Just in case could you list your plugins and check you start up for errors.
Need more info on server, plugins and config setups of tnt controlling plugins. (spigot does but tnt cannons work on my server) Also I need a picture the cannon you have build to see the redstone setup. And a side note TPS issues can mess up redstone.
Yes it is build correctly, i just downgraded bukkit to 1.7.9 and my server to 1.79 aswell and it worked, same plugins same everything just downgraded, it was a bukkit problem