Strange behavior – something like preload

Hello everybody,

I have very strange problem, and I dont know where to look to solve it.
On my wordpress I log every page visit to database. Just simple insert in footer.php. But I have noticed, that there are pages in the log, I didn’t visit. And the timestamp of visit is nearly the same as the page I opened.
So it messes up my statistic a lot.

Recently I added new search widget (my own), which contains just simple textbox and button in a form. When someone submits the form, it takes him by GET to page which process the searching. That is simple PAGE with specific template. On that page, I do another log. And now in the log apears new record every 75 seconds, if I leave the window opened. And it is independet on page which is loaded. That page is in the referer, so it seems that browser submits that form simultaneously. But why? How can I turn it of. Or how can I recognize, that page vas really loaded.

Is that some behavior of wordpress, some caching? Or is it browser issue?
I tried chrome and firefox.

I am really stuck.

Thanks for any advice.