nmap -sP showing hosts is up while it is down

[nmapuseraix <nmapuseraix () o2 pl>]

Hi,

I have been scanning large segments (well... 10.0.0.0/8) and after a long while I get the results showing a lot of full 
bunch of C classes responding as "up".
nmap was run with: -n -sP -T4 -oG outfile
Example results:

Host: 10.33.6.0 ()      Status: Up
Host: 10.33.6.1 ()      Status: Up
Host: 10.33.6.2 ()      Status: Up
Host: 10.33.6.3 ()      Status: Up
Host: 10.33.6.4 ()      Status: Up
(...)
Host: 10.33.6.254 ()    Status: Up
Host: 10.33.6.255 ()    Status: Up
Host: 10.33.7.0 ()      Status: Up
Host: 10.33.7.1 ()      Status: Up
Host: 10.33.7.2 ()      Status: Up
(...)

When I ping (using "ping") those hosts they do not respond to echo.
Running:
nmap -n -sP -T4  10.33.7.0/24
Results in:
Nmap done: 256 IP addresses (256 hosts up) scanned in 0.12 seconds
Timing doesn't seem correct as well, so why is nmap acting like that? Bug? Am I missing something?

--
Regards,
Bart


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