I have created .aspx page on my SharePoint site and inserted within the page HTML button.

Example

    <PublishingWebControls:editmodepanel PageDisplayMode=Display runat=server SuppressTag=True>

...

<button>Click Me!</button>

...

</PublishingWebControls:editmodepanel>

Every time I hit 'Click Me!' the post back occurs. This is not my desired behavior, but I have found a way how to not cause post backs. I added javascript code to onclick property <button onclick='return false;'>Click Me!</button>

My question is, why the post back occurs, even if the button does not contain type=submit property?

I checked also master page, which contains <form runat=server> and wraps all the content and there is also no action=page.aspx property.