I hadn't had time to download...
But do you have "AutoScroll" on or off?
If it is ON, then alClient in a scrollbox is a recursive size loop, afaik. I.e. the Scrollbox should be sizing its clientrect to fit the controls inside, but the alClient, would change its size to the (remainder of the) clientrect of the Scrollbox. So that I would not expect to work. But I don't know if there is a special define for that.
I also don't know how well the scrollbox does with all other ways controls could be aligned anchored, and require space as either a whole or a set of small groups of which the largest would have to be taken. (I did a quick test on akRight, and that seems to kinda work, with some small oddity)