MY lord these is not a bug. 

Please note the following 

If your Fortress l is successfully attacked, you shall receive temporary protection from further attacks. This will apply as follows:

- TWO hours' protection against the league that launched the most recent successful attack;

- ONE hour's protection against all other league.

If a league under protection launches an attack against another Coalition Capital, that Coalition shall lose their protection against the Coalition they have attacked.

NOTE: There are no restrictions on attacking a league fortress that has your league's Flag.

And by the looks of you screenshot it seem that you either had their flag, or your league attacked their league fortress during the protection period.

ok lets deal with the first thing, having their flag,   when you attack someone who has your flag you automaticly get your flag, so while its possible we had their flag for the first attack not for the next 6

now lets look at your second possibility "we attacked back"

you seriously think they attack us, we see it attack them, they see if attack us  back and forth like that  FOUR TIMES EACH WAY   in under 60 seconds??

nope sorry to get 4 attacks in, in under 60 seconds  all 4 would have to be launched within 15 seconds of eachother

lets try some simple math,  they hit us, we see it, hit back, you saying  we could SEE the attack, react to it, and get our forces to their castle in UNDER 15 seconds?

ok lets say that's possible

 now a SECOND round,  THEY see it,  react, launch, boost,   we see it, react, launch, boost  ALL 4 of those separate action have to take place in UNDER 15 seconds so the NEXT round can take place 

also  and if you like  I'll provide screenshots  showing the last THREE attacks  we had ZERO FLAGS,   so for your  successful attack theory to hold water we would have had to have taken at least  ONE FLAG from whomever we hit

let me nip your NEXT thought in the bud,   suppose we launched  at a third party but someone got to it before us and they got the flag so we got NONE

well that would PROVE what I am saying is true because if they got hit before we arrived we would have gotten turned back by their protection

links to last 4 attacks

https://prntscr.com/fjyopq

https://prntscr.com/fjyot9

https://prntscr.com/fjyoyh

https://prntscr.com/fjyp2x

it says in the TOS  to not discuss how a bug can be exploited publicly, if you contact me directly I will explain HOW they did this, or at least how I THINK they did it