Strange thing on this one.
The format for global tables in db.php is:
$table_prefix . "table" so you would have
$table_prefix . 'blogs' for example.
Looking at the code to add additional global tables, it just adds the value onto the array. No problem.
add_global_table($table_prefix . 'table');
However, I found that doing so fails to recognize that table as global. Instead:
Quite interesting. I did notice that the queries flagged specifically were JOINS (between global_table_name and users), but it also puked on non-joins as well, like updating global_table_name without calling any other tables.
I know Andrew's AWOL for the next week or two, but thought I'd make a note.