Doesn't resize terminal windows correctly on zoom

When using the zoom controls in gnome-terminal or roxterm the window is supposed to resize to preserve the number of lines and columns at the new font size. This isn't working correctly; generally the windows become too small when zooming in and too large when zooming out, but there's no overall pattern.

I think this bug is in compiz because I can reproduce it in gnome-terminal and both versions of roxterm (gtk2 and gtk3 which handle sizing quite differently from each other) but not on my other PC with the same version of roxterm but in gnome-shell with Debian unstable.

The bug seems to be harder to reproduce by using the menus instead of keyboard shortcuts, but after a few changes of zoom it happened again. Also, I haven't reproduced the bug by changing the font from the profile instead of by zooming, even though in roxterm the way it updates the vte's font and then resizes the window is almost identical in both cases, and even when I changed the code to remove the difference (which is that zoom resizes the existing pango description instead of creating a new one). So perhaps whether or not the window is focused has some influence?

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: compiz-core 1:0.9.8.6-0ubuntu1
ProcVersionSignature: Ubuntu 3.5.0-23.35-generic 3.5.7.2
Uname: Linux 3.5.0-23-generic x86_64
.tmp.unity.support.test.0:

ApportVersion: 2.6.1-0ubuntu10
Architecture: amd64
CompizPlugins: No value set for `/apps/compiz-1/general/screen0/options/active_plugins'
CompositorRunning: compiz
Date: Wed Feb 20 15:49:52 2013
DistUpgraded: Fresh install
DistroCodename: quantal
DistroVariant: ubuntu
GraphicsCard:
 Intel Corporation 3rd Gen Core processor Graphics Controller [8086:0166] (rev 09) (prog-if 00 [VGA controller])
   Subsystem: Samsung Electronics Co Ltd Device [144d:c0d3]
InstallationDate: Installed on 2013-02-18 (1 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
MachineType: SAMSUNG ELECTRONICS CO., LTD. 900X3C/900X4C/900X4D
MarkForUpload: True
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.5.0-23-generic root=UUID=01057c77-4c95-4b7f-95cb-b1ff24377cee ro quiet splash
SourcePackage: compiz
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 04/26/2012
dmi.bios.vendor: Phoenix Technologies Ltd.
dmi.bios.version: P01AAC
dmi.board.asset.tag: Base Board Asset Tag
dmi.board.name: SAMSUNG_NP1234567890
dmi.board.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.board.version: FAB1
dmi.chassis.asset.tag: No Asset Tag
dmi.chassis.type: 9
dmi.chassis.vendor: SAMSUNG ELECTRONICS CO., LTD.
dmi.chassis.version: 0.1
dmi.modalias: dmi:bvnPhoenixTechnologiesLtd.:bvrP01AAC:bd04/26/2012:svnSAMSUNGELECTRONICSCO.,LTD.:pn900X3C/900X4C/900X4D:pvr0.1:rvnSAMSUNGELECTRONICSCO.,LTD.:rnSAMSUNG_NP1234567890:rvrFAB1:cvnSAMSUNGELECTRONICSCO.,LTD.:ct9:cvr0.1:
dmi.product.name: 900X3C/900X4C/900X4D
dmi.product.version: 0.1
dmi.sys.vendor: SAMSUNG ELECTRONICS CO., LTD.
version.compiz: compiz 1:0.9.8.6-0ubuntu1
version.ia32-libs: ia32-libs N/A
version.libdrm2: libdrm2 2.4.39-0ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 9.0.2-0ubuntu0.1
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 9.0.2-0ubuntu0.1
version.xserver-xorg-core: xserver-xorg-core 2:1.13.0-0ubuntu6.1
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.7.3-0ubuntu2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.99.99~git20120913.8637f772-0ubuntu1
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.20.9-0ubuntu2
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:1.0.2-0ubuntu3