Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 15490)
+++ wp-includes/category-template.php	(working copy)
@@ -713,7 +713,7 @@
 		$tag_id = isset($tags[ $key ]->id) ? $tags[ $key ]->id : $key;
 		$tag_name = $tags[ $key ]->name;
 		$a[] = "<a href='$tag_link' class='tag-link-$tag_id' title='" . esc_attr( $topic_count_text_callback( $real_count ) ) . "' style='font-size: " .
-			( $smallest + ( ( $count - $min_count ) * $font_step ) )
+			number_format( $smallest + ( ( $count - $min_count ) * $font_step ) , 4, '.', '')
 			. "$unit;'>$tag_name</a>";
 	}