2.1 regression: forms: thin line drawn over radio buttons with error

[lookfirst]

<div class="control-group error">
    <label class="control-label" for="inputError">Radio with error</label>
    <div class="controls">
        <label class="radio">
                <input type="radio" id="inputError">
        </label>
        <span class="help-inline">Please correct the error</span>
    </div>
</div>

This produces a weird line above the radio button.

Screenshot:

http://www.evernote.com/shard/s178/sh/2aba8695-bdf5-4ab0-87b7-39f0a281a743/12a1e0343a5717c4086258327731cccc

It boils down to this change in mixins:180

    .box-shadow(inset 0 1px 1px rgba(0,0,0,.075)); // Redeclare so transitions work

[lookfirst]

thanks!