Well I finally solved it properly.

I wrote my own (or rather hacked on the original) TMControlScrollBar and built a TMScrollingWinControl that uses it.

What I ended up doing was just taking out about 2 lines of code from the original (plus a little other cleanup for me)... the TControlScrollBar refuses to separate itself from the ClientHeight no matter what. I needed a scrolling window control that used the scrollbar separately.

I'm sure the better way would have been to embed a TScrollbar within my control, but every time I tried that it crashed... and the TScrollBar seems to not be responding to messages for some reason.

In the process I also changed the range and position fields to be longint so I can handle more transactions with it. Now I can set the range to be equal to the number of transactions, and set the page size according to (clientheight div rowheight) so the thumb works right.