OK, I've found the culprit, and it's the, what should I call it... 'inflexibility' of WP_Query in regard to the MySQL ORDER BY clause, but it's probably my fault because I didn't read WP_Query reference regarding the "orderby" clause more carefully - take a look at the very last paragraph of this section:
In MySQL (I suppose in any other SQL, too), when sorting by multiple fields/columns, you should place a comma between field/column names, like I did in 126.96.36.199 - "menu_order, ID", or ""menu_order DESC, ID ASC"".
On the other hand, when setting 'orderby' value for WP_Query, there should be no commas present in there. And ordering by multiple columns, each having a different ORDER, is, as far as I can determine, not supported (yet).
So, to cut the jibber-jabber, I've uploaded version 188.8.131.52 of the plugin to the repository and it should be available for download now, or as an automatic update in the next 24hrs.
Please let me know if it still doesn't work right for some reason.