Hi,
I must confirm that the "clear log" button does not work as expected indeed. It clears the "Firewall Events" only even when "Connections" are chosen from the drop-down. Sorry for that. Will be fixed in the next release.
About the log flooding - sorry for this as well. Others (mainly Logos and Rednose) have been reporting this for quite some time. These are indeed blocked packets, the problem is that they are logged in such a verbosity. We are still thinking about how should we change this to be more useful. This *is* annoying, I know.
You can disable logs alltogether by editing Config.xml file, in %appdata%\Alwil Software\avast5\fw\ folder. Set the value of LogNoLogos="1". Firewall must stopped when editing this file.
I know it is not a solution, but might be a temporary cure for the growing log file.
Lukas