Summary When a RadPane has Scrolling="Y" (or X/Both) and also has BorderWidth, BorderStyle, BorderColor set (either directly on the pane or via the parent RadSplitter's PanesBorderSize), the pane's inner scrollbar does not render/work correctly. The space reserved for the scrollbar remains in the layout, but the scrollbar itself is missing or non-functional, effectively making the pane's content unscrollable.

Steps to Reproduce

1. Create a RadSplitter with a RadPane that has Scrolling="Y" and BorderWidth="3" BorderStyle="solid" BorderColor="blue" (or just rely on PanesBorderSize).
2. Add enough content to the pane so it overflows vertically.
3. Load the page in Chrome (reproduced on Chrome 152).
4. Observe: only the outer document scrollbar appears; the pane's own scrollbar is missing or the reserved scrollbar gutter space is empty, and the content cannot be scrolled within the pane.

Expected behavior The pane's scrollbar should render correctly and remain functional regardless of BorderWidth/BorderStyle/BorderColor/PanesBorderSize settings.

Actual behavior Scrollbar space is reserved but the scrollbar is missing/non-functional when a border is applied to the pane.