There is currently a bug present which makes it so that whenever aegis is applied to a character and they are struck, aegis will absorb the blow, but it will also interrupt any active skill, be it auto-attack, casts, or even Elite skills. There is also another current report of aegis instead of absorbing blows it will trigger another slot skill (specifically a block skill). From what I can tell this bug is present in both PvE and PvP environments.