I can confirm what Starpest and berardje are saying. While in some cases the problem lies in simple things as Gesten Nyotas here is saying, that isnt the case here..
Whenever i fire a cannon on this particullar skill challenge, any shot, charged or not, end up exploding 1 metre in front of the cannon as if its hitting the castle wall.
This is a bug that prohibits people form getting the map completion on Bloodtide Coast, and consequently world completion alltogether.
Not to mention that it has been like this forr DAYS. It should be brought to the attention of a gamemaster/admin/developer and escalated accordingly.
Silly little bug that irritates me to the point of questioning the fun of it all…