I'm not sure why, because I'm clearly not as clever some people here, but after updating to the latest Avast beta, moving files in XP3 became delayed: I could see the Avast animated icon cycling round on some files, and the CPU fan got a lot noisier. Anyhow, after hunting about I found that Defense+ in Comodo wasn't fully disabled, even though it is checked as disabled. I had already disabled the cloud scanner, because that was still active after disabling D+ but Execution Control settings were also still enabled. Since disabling them all by unchecking everything on the Defense+ Execution Control settings page the problem has gone away. As I said, don't know why it should suddenly show after the pre-release update, but just in case anyone has the same problem you might want to check your Comodo settings.