This is the width in the ui-select class causing your problem. Setting the width to auto should fix the problem. jQM adds a ton of extra markup so that the look on the page is consistent across multiple devices. If you are viewing the page source in a browser, such as Chrome or FireFox, you may see additional elements. In your case, you had to change the ui-select class, since by default it has a width of 60%.
Live example:
JS:
$('#select-choice-1').parent().parent().css('width','auto');
HTML:
<div data-role="page" id="home"> <div data-role="content"> <div data-role="controlgroup" data-type="horizontal" data-inline="true"> <label for="select-choice-1" data-inline="true">Choose Expiry Date</label> <select name="select-choice-1" id="select-choice-1" data-inline="true"> <option value="1">01</option> <option value="2">02</option> <option value="3">03</option> <option value="4">04</option> <option value="5">05</option> <option value="6">06</option> <option value="7">07</option> <option value="8">08</option> <option value="9">09</option> <option value="10">10</option> <option value="11">11</option> <option value="12">12</option> <option value="13">13</option> <option value="14">14</option> <option value="15">15</option> <option value="16">16</option> <option value="17">17</option> <option value="18">18</option> <option value="19">19</option> <option value="20">20</option> <option value="21">21</option> <option value="22">22</option> <option value="23">23</option> <option value="24">24</option> <option value="25">25</option> <option value="26">26</option> <option value="27">27</option> <option value="28">28</option> <option value="29">29</option> <option value="30">30</option> <option value="31">31</option> </select> <select name="select-year" id="select-yaer" data-inline="true"> <option value="2011">2011</option> <option value="2012">2012</option> <option value="2013">2013</option> <option value="2014">2014</option> <option value="2015">2015</option> <option value="2016">2016</option> <option value="2017">2017</option> <option value="2018">2018</option> <option value="2019">2019</option> <option value="2020">2020</option> <option value="2021">2021</option> <option value="2022">2022</option> <option value="2023">2023</option> <option value="2024">2024</option> <option value="2025">2025</option> <option value="2026">2026</option> <option value="2027">2027</option> <option value="2028">2028</option> <option value="2029">2029</option> <option value="2030">2030</option> </select> </div> </div> </div>
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