I have noticed if I cast metabolic quickening and accelerate I am as you would expect affected by both. If I then cast metabolic slowing it removes first quickening and after a second cast of metabolic slowing it removes accelerate.

I know the accelerate help file says it is cumulative with quickening but I was wondering if I only cast accelerate from normal speed what benefit is there from casting metabolic quickening as well when already accelerated?

Also is it a bug that slow removes quickening first then accelerate even though accelerate was the last spell cast on myself?

Metabolic/haste improve offense and defense. Accelerate improves just defense. But you can stack them and have the benefits of both, with the downside your moves drain when fighting.