Placing a leftbound (class=ui-btn-left or -right) select element inside a header (div data-role=header) results in the select element being displayed way to narrow to display its text. The following code works with jquerymobile 1.1.1, yet none of the versions of 1.2:
Thanks for reporting the issue and including a test page.
The issue is caused by a change in the JS. "Option 1" is now wrapped in a span with class ui-btn-left what is not supposed to happen. Temporary work-around is not adding class ui-btn-left to the select itself but wrap the select in a div with that class.
While looking at your test page I also saw an issue with the position of the select button. The button should not have top and bottom margin. Until we fixed this in master you would have to set the margin to 0 with custom CSS.
Here is your test page including the work-arounds: http://jsbin.com/ojanit/6/edit
Select: Remove class ui-btn-left/right from the select element itself…
… during enhancement. Fixes #5073