The search_in variable doesn't seem to be searching both fields in this select statement. So only results from the primary location are being returned I believed. I checked the entries and they do use the secondary field. The second field is a relationship, is that the issue? Thanks in advance.
<select name="work_office[]" name="search_in" value="work_office|work_office_2" class="Textbox4">
<option value=""> </option>
{exp:channel:entries channel="offices" orderby="title" sort="asc" dynamic="no" category="1" }
<option value="{title}&&"" >{title}</option>
{/exp:channel:entries}
</select>