Seems to be across several (if not all) classes, that the actions in your bar reloads faster visually than their tooltip describes, but I noticed it on PUG specifically. For several seconds after the action has visually reloaded it is unavalible, according to the chat log.

Platform: Windows

ISP: Sjöbo Teleservice

Type of Internet Connection: DSL

Internet Connection Speed: Dunno. 5Mbit or 10

Date & Time: All the time (14.30 atm: GMT+1, summertime)

Frequency: Always

Level: 42 PUG

Area and Coordinates: Wherever I go

Party or Solo: Solo.

In-Game Time: No clue

Steps: Noticed it during battle. When I tried to hit my actions as they had reloaded, nothing happened except that the log stated I couldn't use this ability yet.