Time: Any
Frequency: Always
World name: Leviathan
Character name: Sarkden Tepes
NPC name: N/A
Monster name: N/A
Class/Level: Everything/50
Party or solo: Both
In-game time: Any
Area and coordinates: Any
Steps:
1. Open Achievements Window
2. Select Battle
3. Select Frontline
4. Select Achievement "Behind Enemy Lines"
5. Description reads "Guide any of the three Grand Companies to a total of 200 Frontline victories combined."
6. Achievement not adding to win totals correctly when you win(first place) in a Frontlines match.
7. Achievement doesn't update if your current Grand Company has less wins(first place) than any of your previous Grand Companies.

I have confirmed that players who switched to a different Grand Company have received updates to this achievement when their new Grand Company has less wins than their previous one. In one instance, a player had 199 wins as Maelstrom after the 2.5 patch release and achieving 1 win with Twin Adders gave them the 200th win and the achievement.