Encountered this problem several time last night. I was duo-ing mid range NMs. Prior to battle I was proceed with my buffs, which included using Multishot twice. The icon would appear in the bar and I would receive the message "you have notched an arrow" like it should. The other player with me would initiate the battle (is higher level) I waited a bit for them to get hate, then would engage.

What was happening was I would fire only 1 arrow. The icon for Multishot would remain in the bar, additionally, when I went to use the Multishot skill again, I would receive the message "you can't notch any more arrows". Somewhere in the process the game thought I still had 3 arrows notched, but would not fire them.

I did not try to dis engage to see if that would correct the issue...

Character Name: Scytale Small
Server: Rabenastaire
Race: Lalafell
Time: mutliple times during fights from 8-11pm central
Locations: multiple, check NM locations (Cactaur Jack, Alux, daddy long legs, etc)
Computer: Dell XPS
ISP: time warner cable
Speed: fast