Platform: Windows 7, PC version
ISP: BT Broadband
Type of Internet Connection: Cable
Internet Connection Speed: Can't remember
Date & Time: Happened 2nd November, at around 11:30pm GMT.
Frequency: Only seen it happen once, after we killed both Unknown Soldiers, the next spawn was just one (as it should be).
Character Name: Uriko Savari, also seen by Bahn Knakyu and Jewel Myun
Race: Miqo'te (also Miqote for Jewel, and Hyur for Bahn)
World: Saronia
Class/Skill Rank: CNJ 48
Area and Coordinates: Cassiopeia Hollow, cant remember co-ordinates but it's the large room where Unknown Soldier spawns.
Party or Solo: Party of 3.
NPC Name: -
Monster Name: Unknown Soldier
In-Game Time:
Steps:
1. Went into Cassiopeia Hollow to hunt the NM
2. Upon arriving, we noticed 2 of the same NM had spawned (should only be one at a time)
3. After killing both, the game returned to normal and the spawn was correct next time.

It wasn't a problem (was a nice surprise more than anything), but it obviously isn't meant to happen!