The answer I provided will work. The sequence in which you execute commands makes a difference.

Here's the pseudocode:

1 - check the value of ORDER_BY in the block to sort
2 - set it to the opposite order_by
3 - go_block to the block to be ordered, or the parent block if the block to be ordered is a child block.
4 - execute_query;

email your form (just the .FMB) to [email protected] if this doesn't work, and I'll fix it for you.