Question about scan outputs

[David Maynor <dave () erratasec com>]

Has anyone seen this happen before?

Host is up (0.20s latency).
Not shown: 97 filtered ports
PORT   STATE SERVICE VERSION
21/tcp open  ftp?
23/tcp open  telnet  Netgear broadband router or ZyXel VoIP adapter telnetd
80/tcp open  http    Allegro RomPag
er 4.07 UPnP/1.0 (ZyXEL ZyWALL 2)

But when I rerun the scan I getL
PORT   STATE SERVICE VERSION
80/tcp open  http    Allegro RomPager 4.07 UPnP/1.0 (ZyXEL ZyWALL 2)

I looked in wireshark at the caps of the scan and couldn't not find a reason a banner would be broken up like that. Has 
anybody see or heard of this? If not could you point me to the code responsible for the banner handling/storage/display?

Thank you.
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