Windows ScrollView behavior isn't linked to scrollbar visibility

[freakboy3742]

Describe the bug

If you start the scrollcontainer demo app on Windows, the checkboxes definitely control whether the horizontal or vertical scrollbars are visible - but they don't control whether you can scroll.

To Reproduce

When the app starts, it has Vertical on, Horizontal off. If you turn on Horizontal, a horizontal scrollbar (that appears to be about the right size) is displayed. (Interestingly, the "two finger swipe" action doesn't seem to work for me, but I can't work out if that's the fact I'm running in Windows in a VM). If you then turn off vertical, the scroll bar disappears, but you can still scroll vertically (again, in my case, using the touchpad). The menu items don't appear to do anything - so that part is working as expected - but something in the scrolling is still active.

Expected behavior

The ability to scroll on a given axis should be linked to the visibility of the scrollbar.

Environment:

• Operating System: Windows
• Python version: All
• Software versions:
  • Toga: 53a10cf, 0.3.0.dev26

Additional context

There was a broadly similar bug on Cocoa - once the scroll direction was set, the content was set to a specific size, which meant that even if you turned on horizontal scrolling, the size of the content was set to the same size as the scroll window, so there was nothing to scroll. Forcing a refresh corrected that; I did a quick check, and it doesn't look like exactly the same fix works for Windows, but the problem may be in a related area.