This is a somewhat old question, and it already has an accepted answer; I wanted a slightly more fluid design (and my use case doesn't really match yours), so I came up with a different solution, I just wanted to write it here for posterity.
Bootstrap columns are based on float: left , so you get a weird layout when the column wraps and the left column are higher than the right. In this case, the browser tries to put it to the right, if space permits, before moving it to the next line.
You did not want to copy your columns and use visible / hidden classes, however there is another option for using visible / hidden classes that use the fact that these are floating containers. CSS has the clear property to force the container to move below all floating containers (the left value moves it below all left floating, <T23> below all right floating and both below all floating, left or right), so you can insert the following between your columns:
<div class="visible-sm visible-xs" style="clear: both;"></div>
You will get the same effect, but with less complexity, although perhaps not the most kosher way to download.
falstro
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