Line number button in mode line wrongly drawn

[era]

Binary package hint: emacs23

When you hover with the mouse over the line number indicator in the mode line, it is supposed to turn into a clickable button. But the button's east border is drawn in the middle of the button, obscuring the line number and somewhat losing the illusion of a clickable button.

I am attaching a screen shot illustrating the problem. Notice the odd vertical bar which is partially overlapping the line number underneath the cursor.

It looks like the button's geometry was decided based on just the letter "L" and missing the fact that the line number is dynamically updated to display after the "L".

 era@lucid:~$ lsb_release -rd
 Description: Ubuntu 10.04.1 LTS
 Release: 10.04

 era@lucid:~$ apt-cache policy emacs23
 emacs23:
   Installed: 23.1+1-4ubuntu7
   Candidate: 23.1+1-4ubuntu7
   Version table:
  *** 23.1+1-4ubuntu7 0
         500 http://mirrors.nic.funet.fi/ubuntu/ lucid/main Packages
         100 /var/lib/dpkg/status