I haven't tested this with other skills, but it seems foraging is bugged. When the player uses the hotbar to process requests, the player is able to send instructions to start fishing, then (when fast enough) start a forging.
The game client however doesn't allow both to succeed, and the fishing (the first process) is the only one that completes.
It seems to be any skill that processes a action. Process fishing and press the hotkey twice, and it will cast the line twice - again, only the first one is completed.