Is the first step of most the accepted mechanism of Perkin's reaction correct?

If I am not wrong this is the most accepted mechanism of perkin's reaction:
[![enter image description here](https://i.stack.imgur.com/H82ML.png)](https://i.stack.imgur.com/H82ML.png)


In the first step, is the acetate ion basic enough to abstract proton from acetic anhydride?
If yes, I have a counter arguement. It is well known that acetic anhydride doesn't answer iodoform test despite having an acetyl group. It is mainly because, abstraction of proton is not possible as it would produce a unstable carbanion (because of cross conjugation). 
If OH- cannot abstract the proton iodoform rxn. , how could acetate ion which is a weaker base abstract the same proton in Perkin's reaction?


