Hi, Robert -

The functionality of the built-in scroll bars in windows and in user objects can only be customized in a limited manner. This may be why I've never used them in my almost 30 years as a PB developer. I cannot say with certainty that it is not possible to do what you have asked with the built-in scroll bars, but I doubt that it is possible.

In my reply to another question you asked a month ago, I referred you to a different, but similar question where I had provided a small example app that shows one way how this can be done with a custom visual user object and a vertical scrollbar control.

Your earlier question: 
    https://community.appeon.com/index.php/qna/q-a/scroll-position-of-user-objects

The other question that contains the sample app:
    https://community.appeon.com/index.php/qna/q-a/how-to-scroll-vertically-on-user-object-using-powerscript

Best regards, John

Hi Robert;

  I suspect that at some point, the App users need to scroll all the way down. So blocking that feature when a certain object get to the top of the Window scrolling area seems to be a weird behaviour to need.

  Why not use two User Objects, DataWindows or one DWO (using a fixed header band of objects not for scrolling) where the "don't let it out of your sight" objects are in one control / area and the all scroll-able objects are in the 2nd control / area. Then only the 2nd control (for User Objects / DC's) is scroll-able leaving the 1st control always viewable (that is, no window scrolling now required.

Food for thought.  HTH

Regards .. Chris