After a failed import (column match), subsequent attempts fail with the error "Column match with this Column name and Import setting already exists" on several fields. i'm not sure yet which fields they pertain to, as they all look like this:
<ul class="errorlist">
<li>__all__
<ul class="errorlist">
<li>Column match with this Column name and Import setting already exists.</li>
</ul>
</li>
</ul>