Easiest way to see this is to list directories using 'ls' with more than 30 files. Using gnome-terminal, the last 29 lines of stdout are correctly printed. The first lines are replaced entirely by whitespace.
Using Xterm does not show this problem - all files are listed.
Unity is in use as my desktop under Ubuntu 11.10.
I have also seen this problem with 'diff'. If too many lines are output, the first few are replaced by whitespace.
I made a slight change to the default gnome-terminal profile, to set the scroll back lines to 5120. I do not know whether this problem occurred before altering the profile. I have however since set this back to the default 512.
ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: gnome-terminal 3.0.1-0ubuntu3
ProcVersionSignature: Ubuntu 3.0.0-12.20-generic 3.0.4
Uname: Linux 3.0.0-12-generic i686
ApportVersion: 1.23-0ubuntu3
Architecture: i386
Date: Wed Nov 2 10:43:16 2011
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111012)
ProcEnviron:
LANGUAGE=en_GB:en
PATH=(custom, no user)
LANG=en_GB.UTF-8
SHELL=/bin/bash
SourcePackage: gnome-terminal
UpgradeStatus: No upgrade log present (probably fresh install)
I've seen this kind of problem when my disk was full. Since gnome-terminal stores the scrollback buffer in a (deleted) file in /tmp, when the disk fills up, scrollback gets lost.