Applying the input-block-level class works great for me, across various screen widths. It is defined by Bootstrap in mixins.less as follows:
// Block level inputs
.input-block-level {
display: block;
width: 100%;
min-height: 28px; // Make inputs at least the height of their button counterpart
.box-sizing(border-box); // Makes inputs behave like true block-level elements
}
This is very similar to the style suggested by ‘assembler’ in his comment on issue #1058.