Field labels do not display in location edit form.

I am using 6.x-3.x-dev (2010-Jun-13) and this recent problem has not been mentioned in any issue I can find. I believe it may be a css issue, but it happens on several D6 sites, with different themes.

When a user goes to create or to edit a content type with a location, the field labels fail to display (Except for 'Country:'). The page code appears to be correct:

<fieldset class="location collapsible collapsed"><legend>Location</legend>

<div class="form-item" id="edit-locations-0-name-wrapper">
 <label for="edit-locations-0-name">Location name: </label>
 <input type="text" maxlength="64" name="locations[0][name]" id="edit-locations-0-name" size="64" value="" class="form-text" />
 <div class="description">e.g. a place of business, venue, meeting point</div>
</div>

...

It is as if there is a label {display:none;} hidden in the css somewhere, but if this is the case, why does the 'Country' label display.

The input fields work correctly, but the user has no way of knowing what to enter where. Even Phone: and Fax: are displayed as unlabeled input fields. The problem is limited to the Location edit form, and has me stumped. Has anyone else seen this, or does anyone have any idea where to look?