If a party member is targeted and he vanish for some reason, the member marker at party widget will stay there until you're able to target that member again. Until then the marker will stay stuck at that member's name and a second marker will be generated for current usage, leaving the party widget with 2 markers.

Platform: PC
ISP: BrTurbo
Type of Internet Connection: ADSL
Internet Connection Speed: 2MB
Date & Time: -
Frequency: always
Character Name: Lienn Deleene
Race: Miqo'te soS F
World: Istory
Class/Skill Rank: -
Physical Level: 50
Area and Coordinates: -
Party or Solo: Party
NPC Name: -
Monster Name: -
In-Game Time: -
Steps:
1: Join a party.
2: Target a party member.
3: Have this party member vanish (not only walking out of target range...vanish like using return, teleport or walking into a area zone, where everyone vanish until reload is done. An easy way to see this is targeting a party member and they both walk in or out of a city)
4: The target marker at party widget (the yellow marker) will stay at him even though you're not targeting him anymore. It will stay that, stuck, until you're able to target that member again...if you try and target a different party member it will generate a second marker, leaving you with 2 party members with the yellow marker.