First of all, I don't know if this is a bug, per se. On 5.3.175888.1227 I noticed a performance hit when using my backup software, XXClone, but not during regular operation. I did not attribute this to CIS. However on 5.4.189068.1354 the backup slowed way down so I had to look into it. I found cmdagent CPU usage very high and turning off Realtime AV got it back to normal. I also checked it during regular operation and it seemed to be active more than I would expect, although not to the level of being a nuisance. This is not a complaint, CIS may just be doing what it's supposed to be doing. Except that I would expect not so much CPU usage for Trusted and Safe programs & files. Is this expected behavior? As for backups, I now know that I need to turn off Realtime first.
XP Pro SP3 x86
Athlon64 3800+ (single core)