With the types of window that sport the larger titlebars (example shown below) maximized window dragging only works for the top approximately 20px whereas the titlebar is in fact closer to 55px in height
After reviewing this, there doesn't appear to be a reliable way to detect whether a window has a large titlebar or not. For now, You'll just have to make sure you click in the top 80% of the titlebar.
Isn't maximized windows dragging native to Windows 7?
No, you have to forcibly drag the window to the top of the monitor (which isn't always possible) not just "drop" on the desired monitor as per DisplayFusion's design
EDIT: Also isn't this more of a "Postponed" rather than "Complete"?
Although we haven't been able to find a way to fix this issue yet, it's on our internal list of bugs to follow up on, so for the purposes of the forum, it's completed, and hopefully we'll have a fix for it in a future version.