Not completely sure if it is a bug, but if it is displayed on the Minimap shouldn't it be on the big map too? It's the "Hail to the King, Kupo" Quest.

Isp: Kabel Deutschland
Internet Connection Speed: ~12.5MB/s
Date & Time:8:26 pm GMT+1
Frequency: Once
Charactername: Kira Kite
Race: Miqo'te
World: Odin
Class/Level: Bard 50
Area and Coordinates: Old Gridania 8X 11Y
Party or Solo: Solo
NPC Name: Silent Conjurer
Monster Name: N/A
Steps:
1 Accepted Quest
2 Went to Old Gridania
3 No Questmarker on the big map