Black Mage non stop spell interruption

Resubmitting with more info as asked in http://forum.square-enix.com/ffxiv/t...l-interruption

Time: 11:46am
Frequency: Sometimes
World name: Tonberry
Character name: Qoo Kitty
Monster name: Puk Hatchling
Class/Level: BLM/50
Party or solo: Party
In-game time: 10:41pm (Eorzea Time)
Area and coordinates: Western La Noscea (27,24)
Steps:
1. Form party with Chocobo at free stance
2. Attack monster A, Chocobo will also be attacking monster A
3. Wait for monster A to be low, then cast Fire I
4. When monster A is killed by Chocobo before Fire I is finished casting, the word INTERRUPTED will appear, Fire I will be canceled
5. Trying to attack other monster with Fire I will be INTERRUPTED and canceled few times in consecutive.

How the INTERRUPTED looks like in game:
http://i.imgur.com/9atGUqe.png?1

Connection Specs
- 300mbps fiber connection

PC Specs
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Browser Information
- Name and version of the browser currently in-use: Firefox 31.0