Doing a full scan with Avast will gobble up memory as it continues to scan. I wanted to do a full scan, then Avast would scan new files, which I thought would be the best protection. I got around the problem by creating 4 separate scans. I have watched memory with the app, Memory Diag and File Cache continues to grow during the full scan and all 4 of the separate scans I created.
If you need any other info from me that could help solve this bug let me know.
Avast is running on an iMac 27-inch, 3.5 GHz i7, and 16 GB of ram.