Opera - webApp slides up when button pressed

I am developing this web application and I have came across a "little" problem in Opera 11.01 browser. When I press any <button> on the app, the page slides up.

To rep开发者_StackOverflow中文版roduce (the system is in Polish, so follow the steps):

1. Go to https://postplus.pl/demo .
2. Press "Zaloguj" (the button with green tick icon).
3. When logged in, press the button "Nowa" (or any other button on the left panel).

What is happening?

Not so much.. works fine for me in Opera 11.10

This is an Opera bug (for some reason thinks the element is off-screen and must be scrolled into view or something). A fix is implemented so I suggest you simply try to ignore this issue. While Opera users upgrade, fewer and fewer of them will be affected by the problem.

I have replaced all the <button> tags with <a> tag (with proper styling). It is only solution that came to my mind.

Thanks for the help though.