This is why you are supposed to leave the BsH on allow and not ask, the shield was only first implemented in the 5.1 version's and is in passive mode, basically collecting information for avast to build these whitelist's.
Once the 6 version's come out of beta it should be working properly, but if there is something that is not known by the shield you will still get the alert as this is what it is supposed to do.
If you dont want the alerts either set the shield to allow or add the alerted program or file to the trusted list.