Bug on history control, don't erase no dups

[B]

Hello,

I have the following lines on my login script, intended to make my history big
enough for me, and not to waste space by keeping several copies of the same
command again anda again:

HISTCONTROL='ignoreboth:erasedups'
HISTSIZE=4096
HISTFILESIZE=4096

To make sure it is working as that, I do (where "$" is shell prompt):

$set | grep HIST

This outputs:

HISTCONTROL=ignoreboth:erasedups
HISTFILE=/path/to/my/.bash_history
HISTFILESIZE=4096
HISTSIZE=4096

Part of my history is, righ now:

  522  cd /var/tmp/; touch z
  523  cd /var/tmp/; touch z
  524  ll
  525  ssh zabu
  526  ssh ximi
  527  ls
  528  ssh zabu
  529  ssh ximi
  530  gprolog
  531  GLOBALZS=100000
  532  gprolog --q="[test]"
  533  gprolog --q "[test]"
  534  gprolog --q "[tp]"
  535  ssh ximi

As you see, there are several repeated lines. Many of them are commands I use
constantly. I started with a clean history. But even if not, the duplicates
should have been erased, as I understood from the manual page?

I suspect that, if I am not making any stupid mistakes, is it because I use to
keep several shells opened at once. I open and close them in a semi-chaotic 
fashion.

Do you sugest anything, or is this really a bug?

Also, you may give me some advice on how to reproduce the bug, if what I told
isn't that usefull for finding the problem.

Bashbug script didn't work for me. I think it couldn't find vim on the right
place. I tried making a copy of the script and changing the path on the file
(wich I thought to be trivial), but there is no "vim" written in there either,
so I gave up. o:)

Kindly,

B