One scans more files than the other (if you did a default scan). A full scan should list every file on the PC they are set to scan. The programs may also have different exceptions setup.
Object and Items are the exact same thing. Like "stuff" and "things".
Running 2 anti-virus programs at the same time (actively) is not good, every vendor recommends against it. Running a scan with 2 is OK, but you don't want both to be resident at all times.
Both programs ran 'Full' scans separately; not together. After Kaspersky did its thing, I closed it and then ran MSE. My experience with these programs is that they 'catch' different malware at different times. That's why I have both.
I am aware of the issues with 2 AV programs loaded; one will think of the other as a virus. (like having 2 girlfriends; make sure that they don't meet!). So far, things are working out well for me on 1 Win7, 1 Vista, and 1 XP, computers.
How many files do you have? Include all attached devices and networked drives in the count.
Kaspersky may be skipping memory, paged data, system restores and hibernation data?
Just two internal drives. 80 GB C: drive with the OS (XP Pro), and a 500 GB D: drive that I added, for data.
And in both scans, I selected 'Full scan', and I could see both drives being scanned when I periodically went over to check the scans.
No external drives - No USB flash drives - No DVD in the DVD drive - No networked drives. Just C: and D: internal drives.
Just out of curiosity, I will check the Objects/Items count when I run the scans on my i7 computer. Most people have just one AV program, and that is probably why this type of discrepancy has not been noticed in the past.