Editors crash scrolling file with long lines

I have experienced this problem with Gedit (standard Ubuntu 5.10 installation)
and with Bluefish 1.04 (compiled on my dual opteron), so it might be a gtk problem.

A file with long lines - e.g.:-

http://www.psr.keele.ac.uk/area/uk/ge59/maj.htm

will cause the editors to crash if you try to scroll down the document by
dragging the scroll bar down with the mouse.

In the terminal, Bluefish gives:-
(bluefish:15351): GdkPixbuf-CRITICAL **: gdk_pixbuf_new_from_file:
assertion `filename != NULL' failed

(bluefish:15351): GdkPixbuf-CRITICAL **: gdk_pixbuf_new_from_file:
assertion `filename != NULL' failed the dir_icon and unknown_icon items
in the config file are invalid The application 'bluefish' lost its
connection to the display :0.0; most likely the X server was shut down
or you killed/destroyed the application.

While Gedit gives:-
The program 'gedit' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadLength (poly request too large or internal Xlib
length erro'. (Details: serial 30590 error_code 16 request_code 1
minor_code 0) (Note to programmers: normally, X errors are reported
asynchronously; that is, you will receive the error a while after
causing it. To debug your program, run it with the --sync command line
   option to change this behavior. You can then get a meaningful
   backtrace from your debugger if you break on the gdk_x_error()
function.) Terminated

I'm using 2.6.12-9-amd64-k8-smp, Ubuntu 5.10, gtk 2.8.6-0ubuntu2.1