Fixed #1831

See it in action here http://jsfiddle.net/wwx7ez74/4/ with IE10+

src/definitions/modules/dropdown.less

@@ -395,6 +395,12 @@ select.ui.dropdown {
   display: none;
 }
 
+@media all and (-ms-high-contrast:none) {
+  .ui.selection.dropdown .menu {
+    min-width: calc(100% - 15px);
+    }
+}
+
 @media only screen and (max-width : @largestMobileScreen) {
   .ui.selection.dropdown .menu {
     max-height: @selectionMobileMaxMenuHeight;