Index: wp-admin/includes/plugin-install.php
===================================================================
--- wp-admin/includes/plugin-install.php	(revision 20636)
+++ wp-admin/includes/plugin-install.php	(working copy)
@@ -127,6 +127,8 @@
 			<option value="author"<?php selected('author', $type) ?>><?php _e('Author'); ?></option>
 			<option value="tag"<?php selected('tag', $type) ?>><?php _ex('Tag', 'Plugin Installer'); ?></option>
 		</select>
+		<?php else: ?>
+		<input type="hidden" name="type" value="term" />
 		<?php endif; ?>
 		<input type="search" name="s" value="<?php echo esc_attr($term) ?>" />
 		<label class="screen-reader-text" for="plugin-search-input"><?php _e('Search Plugins'); ?></label>