I have just hit the same issue where my scrollview panel would not update its height.
I am not sure if this is caused because the scrollview was added using the designer but I found a different solution.
I am adding items to the scrollview using a sub routine called in Activity_Create, inside my sub routine is where I am adding items and was trying to update the scrollview.panel.height but nothing would work to adjust the size so I took the scrollview.panel.height out of my sub routine and added it directly to the Activity_Create and it started working as expected and updated the height correctly everytime I fire the activity. As soon as I move scrollview.panel.height back into my sub it stops working again and just uses the default set in the designer.
Strangely it does seem to work in other parts of my app but they are not as dynamic as the one I had issues with.
Not sure if this is a bug but thought I would mention it