Using a subquery as the table argument in the from() call used to work fine, like so:
$select = $db->select();
$select->from("(select people.id from people)", "count(id)");
I know there are cleaner ways to get the same result, but this is a simplified version and in some cases it is necessary to do a select like this, for example when doing your own pagination you may want to put the sql from one query into a call like this to find out the number of rows returned from it.
When doing this, if the code in the table argument contains a period, the new schema code on line 358 in Select.php will break the query:
// Schema from table name overrides schema argument
if (false !== strpos($tableName, '.')) {
list($schema, $tableName) = explode('.', $tableName);
}