Limiting the submissions doesn't work right for anonymous users

I created a new form, a simple questionnaire with two options (http://tormu.ignorelist.com/temp/test)
Option settings are 1|Syyllinen 2|Syytön (quilty, non-quilty in Finnish, nevermind)
Advanced settings: Limit 1 submission(s) per hour

Then I log out to be an anonymous user, and vote - it's ok.
Then I go to the same URL with another computer with totally different IP and try to vote: error "You have submitted the maximum number of entries. Check submission guidelines."
I try the same address with my mobile phone and get the same error.
I log in from the second computer and vote - it's ok.

Then I clear the results so it's back to start. I vote with my mobile phone browser and then wait about 30 minutes before even trying with computer, and then it works.

Tried the same thing with cache off and it didn't matter.

Attached file is a shot of the results. As you can see, most of the submissions are about 30min away from each other. When I set the limit to "Unlimited", this doesn't occurr - I got 30 submissions in first 10 minutes.

Running the cron.php didn't seem to solve anything either. The same ~30min pause between any anonymous user appears on a server with not running the cron at all and didn't go away if I ran it manually in 5min intervals.