strange 404 (when i submit form method=get) (UPDATED)

[eluser]molodoy[/eluser]
Hi all

My app is needed multiply checkboxes input.
There is 404 error appears when I submit form.
URL in this case looks like: http://site.tld/autosalons/?auto[]=260
Now, if i just put cursor in URL field of my browser and hit Enter, right page appears!

I've checked HTTP-headers.
When I've submitted form and 404 err:

Code:

GET /autosalons/?auto[]=288 HTTP/1.1

upd: forum changes url! "[" in url looks like % 5 B (without spaces) and "]" looks like % 5 D

When I hit Enter and all works fine:
GET /autosalons/?auto[]=288 HTTP/1.1


How can fix it?