RSE "Filter Strings" Dialog Usability

This dialog must be one of the strangest and most incomprehensible Windows dialogs in any Windows application anywhere. I am always puzzled by:

1. The flow of control: How the buttons and dropdowns work, how they're related to one another, in what sequence they should be used.
2. The display: The list box showing the defined Filter Strings is horizontally scrollable (which is bad in itself, but may be unavoidable); widening the window doesn't widen the list box, but instead widens the buttons (now THAT'S helpful!), the dropdown boxes, and the white space!

I just cannot understand how such a design came to fruition. Wasn't this tested on animals first?

Try just about anything. Here's one:
1. Select an existing filter string, e.g. JAGLIB/QCPYLESRC(*) MBRTYPE(*)
2. Under "Member types to subset by" select "SQLRPGLE" in the Member type dropdown.
3. Click the "Add" button.
4. Click the "Apply buton.
5. "MBRTYPE(SQLRPGLE)" should replace "MBRTYPE(*)" in the filter string (but you'll have to scroll right to see it).
6. Click to highlight this modified entry under "Filter strings".
7.Under "Member types to subset by", click to highlight SQLRPGLE in the listbox.
8. Click the "Remove" button.
9. Click the "Apply" button.
10. Error: "Filter string already exists". (When I'm REMOVING a filter?!)
11. Click the "Revert" button.
12. Click to again highlight this modified entry under "Filter strings".
13. Under "Member types to subset by" select "*" in the Member type dropdown.
14. Click the "Add" button.
15. Error: "Member type SQLRPGLE is already specified".
16. Click the "Revert" button.
17. Click to again highlight this modified entry under "Filter strings".
18. Under "Member types to subset by" select "*" in the Member type dropdown. "*" is highlighted.
19. Click the "Apply" button.
20. Error: "Filter string already exists". (The "*" string already exists? That's what was highlighted when "Apply" was pressed.)
21. Click the "Revert" button.
22. Click to again highlight this modified entry under "Filter strings".
23.Under "Member types to subset by", click to highlight SQLRPGLE in the listbox.
24. Under "Member types to subset by" select "*" in the Member type dropdown. "*" is also highlighted, and all three buttons (Add, Change, Remove) become available.
25. Click the "Add" button.
26. Error: "Member type SQLRPGLE is already specified".
27. Repeat steps 21-24.
28. Click the "Change" button. The highlighted listbox entry changes from "SQLRPGLE" to "*".
29. Click the "Apply" button.
30. Error: "Filter string already exists". (What? The existing filter string appears to be "SQLRPGLE", not "*"!)
31. Repeat steps 21-24.
32. Click the "Remove" button. The listbox entry changes from "SQLRPGLE" to "*" but is not highlighted.
33. Click the "Apply" button.
34. Error: "Filter string already exists".