If a button tag is used in the header toolbar then it will increase the height of the header toolbar because the title is displayed in a new line. Using anchors shows the expected behavior. According to http://jquerymobile.com/test/docs/toolbars/docs-headers.html any valid button markup should work. (-> "Each button is typically an anchor element, but any valid button markup will work." ).
The reason why I want to use the button tag is because it's semantically more correct than an anchor and it can easily be disabled/enabled.
Thanks for reporting the bug.
I will add "button" to the selector that now only contains the anchor element. Maybe the docs need to be adjusted a bit as well, because this functionality is not supposed to work for form buttons.
In the meantime you can fix it by adding class "ui-btn-left" to the button element in your markup.
Header buttons: Added "button" to the selector. Fixes #4638 - Using b…
…utton tag in header will show title in new line [1.1.2.]