If the web accelerator uses a proxy to achieve this acceleration, then yes you would have to uncheck it in order for the local traffic to be scanned.

However, what build of avast do you have, the latest is 6.0.1289 and there is a new feature in that, were it scans all HTTP traffic ?

So I don’t know how this would impact on the accelerator function, if it scans it by default then there may be no need to uncheck that Ignore local communication option.