Simple but usefull trick in pvp .
~ applies only on tactical trooper
~even you use zzz combo 3 times and follow up siege shelling the combo will still continue .
~ a simple mana break will do to counter it (most players mistake is they dont mana break because they're thinking that the combo will just end like other combos, but unfortunately Siege shelling miraculously ignores the knockdown rate.
~ and I think its a bug :P