There is an issue regarding the how items such as Repulse mantle and Vocane ring affect knockback when multiple players are hit. It may be be summarized as follows under the given conditions.

If for any reason a player has a resistance to knockback and is in AoE range of another PC who does NOT have that same resistance, they are knocked back the unreduced distance when the a knockback area attack hits the person NOT wearing the anti-knockback gear. Furthermore, knockback will occur on ALL players even if not all are hit with the attack, regardless of gear.

Platform:
Windows

ISP:
Cox

Type of Internet Connection:
LAN

Internet Connection Speed:
130 Mbps

Date & Time:
April 20, 2015

Frequency:
State how frequently the issue occurs. Please select from the following.

For me, I have always experienced the issues under the outlined conditions. Others who have reported to me claim that it is intermittent.

Character Name:
Sephiran

Race:
Hume M

World:
Bahamut

Main Job:
Paladin

Support Job:
WHM

Area and Coordinates:
Cirdas Caverns [U], Outer Ra'Kaznaar, Morimar Basalt Fields

Party or Solo:
Party

NPC Name:
None

Monster Name:
Ironclad, Dakuwaqa, Tojil, Muyingwa, Matamata

Steps:
Engage an enemy with radial auto-attacks (like matamatas or ironclads) that inflict knockback or an enemy with special moves that inflict knockback while wearing Repulse mantle or Vocane ring. Have another player who is not wearing those items step into range of the attacks or summon a luopan. The effect may be observed when the knockback attacks occur.