Opening one line: web client execute a global search

Here is the steps to reproduce the bug but this bug is probably more generic than this example.

I open a partner. I open it's sale.order by clicking on a relate button on the right. I choose one of it's sale.order.

This sale.order has 5 lines. I try to open one of it's line and I have to wait several minutes before the popup opens.

Looking in the server log, I see that ALL sale.order.lines are searched for:

[2010-03-12 10:48:40,234] Level 9:params:[01]: ('db2',
[2010-03-12 10:48:40,234] Level 9:params:[02]: 1,
[2010-03-12 10:48:40,234] Level 9:params:[03]: 'psw1',
[2010-03-12 10:48:40,235] Level 9:params:[04]: 'sale.order.line',
[2010-03-12 10:48:40,235] Level 9:params:[05]: 'search',
[2010-03-12 10:48:40,235] Level 9:params:[06]: [],
[2010-03-12 10:48:40,235] Level 9:params:[07]: False,
[2010-03-12 10:48:40,235] Level 9:params:[08]: False,
[2010-03-12 10:48:40,235] Level 9:params:[09]: 0,
...

and since there are more than 500000 lines, it takes a very long time.