Oh whoops, didn't realize I hadn't done this yet.

Platform: PC
ISP: Time Warner
Type of Internet Connection: Cable
Internet Connection Speed: 1MB down/2MB up
Date & Time: Can happen at any time
Frequency: Random
Character Name: Renta Hamster
Race: F. Hyur
World: Lindblum
Class/Skill Rank: THM 50
Physical Level: 50
Area and Coordinates: Camp Broken Water
Party or Solo:Party
NPC Name: N/A
Monster Name: any
In-Game Time: any
Steps:
1. Cast Shadowsear
2. Shadowsear icon on the action bar doesn't change show the cooldown timer.

*Since I've only observed this happening at Camp Broken Water, it may have something to do with overcrowding and lag.