drupalGet or drupalPost give incorrect 'Ending URL' while 'GET request to' is correct and the site is working fine

I tried to get following URL from both functions:
$this->drupalGet('node/add/event?gids[]=' . $this->node_group->nid);
that should result:
node/add/event?gids[]=9

however they result:
node/add/event%3Fgids%5B%5D%3D9

my apache understands
node/add/event?gids[]=9 or
node/add/event?gids%5B%5D=9
not the result (Ending URL:) (also in my verbose page it sais: GET request to: node/add/event?gids[]=9)

When I use my site and click on my links my site works fine. So Im just wondering what code creates this and I guess there's bug in it because of the result.