In the bootstrap.css, the visible-xs class is identical to the visible-sm class. visible-xs is missing the following:

@media (min-width: 400px) and (max-width: 767px) {
.visible-xs {
display: none !important;
}
tr.visible-xs {
display: none !important;
}
th.visible-xs,
td.visible-xs {
display: none !important;
}
}

Comments

Status:Active» Closed (won't fix)

The Bootstrap 3.0 issue queue is located: https://github.com/twbs/bootstrap/issues

This is the Drupal base theme integration project, which does not actually have Bootstrap code in it.