Guild Wars 2

This is really annoying : the invulnerability. Especially when it happens when it should NOT :
Our server (me included) are attacking the main camp of the ennemy server in WvW. Some archers fire at us from a ledge a bit higher. Can’t jump up to it, but we still see them clearly. One is using a mortar. The situations is : everyone except the mortar is invulnerable. Just why are they INVULNERABLE?

Another annoying thing : i know there is a skill to pull ennemies to the caster, which is ok. So why can the caster cast it on players that aren’t visible on walls or ledges when i can’t use my bows in the same situation? Lag or bug? This gives the ennemy unfair advantage they’re more than happy to take advantage of.

Edit : the invulnerability thing happens too much even with normal mobs, even if they’re attacking me in close range.