Click-dragging in space to right of vertical scroll bar caused window to be moved

The picture above shows that you have moved the cursor too far to the right. Once you move it over there the OS believes that you want to resize the window.

It's not a bug but a deliberate design feature that was introduced a few versions of OS X ago. The former action was that you had to move the cursor to a corner of a window to resize, Apple chose to change that behaviour to be able to resize anywhere, which is a more obvious way to do it if you use trackpads, but not necessarily if you use a mouse.

With Scroll Bars set to be visible all the time, like in your screenshot, the scroll bar is quite narrow.

Changing the setting in System Preferences > General to 'Show when scrolling' displayed a wider scroll bar if you move the cursor into that area when it is showing, like in Duane's screenshot above.

Depending on your setup, this setting may make it easier to drag the scroll bar rather than resize the window.

Fine for those who want this, even if it's the default, but I would like the option to turn it off. I consider this a negative "feature".

Submit Feedback to Apple here. You never know, they may change the implementation of the feature based on your feedback,

http://www.apple.com/feedback/macosx.html

Anyway, I made that suggested change in general preferences, and the scroll bars disappeared altogether, so that didn't help.

As I said in my previous post,

Changing the setting in System Preferences > General to 'Show when scrolling' displayed a wider scroll bar if you move the cursor into that area when it is showing, like in Duane's screenshot above.

The scroll bar will not be displayed when there is no scrolling required, however, once you start to scroll the bar appears AND if you then move the cursor into the scroll bar area, the bar widens and is wider than in your original screenshot, so it may be of more help to you.

Yes, it is a workaround, bit it's probably the best one available at the present time.