I see two ways that your newly added records might be excluded from the value list.
z_sortORder_bySpaces might be empty or the value of this field might not be unique.
Thus, I'd examine how this field computes or is assigned the spaces that produce the desired arbitrary order to your value list.
phil... please don't take this the wrong way...
but i think i love you... you're a genius! i spent way too much time trying to figure it out and that was exactly the problem (and exactly why the drag and drop sorting fixed it because it re-serialized the sort order every time). somewhere in the back of my mind i vaguely recall something something about duplicate values not being repeated in value lists, but it would never have occurred to me that duplicate values in the second field would hide unique values from the first field... at least, i think that is what you are saying is happening. in any case, simple fix and all is working great. you're the best!