Thunderbird Portable on different machines

Hi folks,

I am running Thunderbirds 2.0.0.19 on an old laptop hard disk which I plug into the usb port of a laptop and a desktop. I am experiencing strange fonts when I run Thunderbird Portable on a my desktop.

The laptop is Dell Latitude 1400 by 1050, 96 dpi screen where Thunderbird
displays just fine and a generic desktop 1280 by 960, 96 dpi, where the
message pane displays what looks like the first subject over the second
subject and so on down the pane. This 'double display' of the text in both the Subject column and sender column makes it essentially unreadable.

Any solutions?
Any one else seeing this?

Have tried changing the screen resolution on both the laptop - where the
changes to the screen parameters does not make any difference (does not cause the problem) - whilst the desktop changing the screen parameters does not resolve the 'double display'. (Unfortunately I cannot set both machines to the same values due to differences between the screen drivers.)