Healing spell glitch

ISP:
Century Link

Type of Internet Connection:
DSL

Internet Connection Speed:
12 Mbps

Date & Time:
11/17/13 10:39 pm PST (though it happens on a daily basis)

Frequency:
Sometimes.

Character Name:
Rina Acevedo

Race:
Race of your character when the issue occurred.
Hyur F.

World:
Siren

Class/Level:
White Mage level 50.

Area and Coordinates:
Various maps such as Wanderer's Palace.

Party or Solo:
Party.

NPC Name:
None.

Monster Name:
Various monsters in Wanderer's Palace such as Tonberries, Buzzards, Tonberry King, etc.

In-Game Time:
10:39 PM

Steps:
Tank and DPS were battling random mobs of Tonberries/Bronze Beetles/Soldiers of Nym/Cog Oils/Corrupted Nymians/Pug Pugils/Gear Grease/Corrupted Nymian Curates. While tank was getting damaged, I had him selected in order to use Cure 1 on him. During these battles, sometimes the Cure 1 spell would not heal the tank despite me having it set to heal him, and would heal myself instead even though I wasn't selected. It would also do the same thing if I tried to heal a DPS at times.
*I am not using any macros due to not knowing how those work, so I never messed with the options.*

PC specs:
OS: Windows 8
Processor: AMD A8 - 5500 APU with Radeon(tm) HD Graphics 3.20 GHz
RAM: 6.00GB
System Type: 64-bit Operating System, x64-based processor