Comment 1 for bug 1650474

When the window is semi-maximized in the corner, the maximize button works as a "restore" button; so what you should see is that the window ought to land in the place where it had previously been before the drag operation started.

Locally I can't reproduce any odd behavior but since you have a somewhat outdated unity8 version, would you mind adding the stable-phone-overlay[1] and try again? Thanks

[1] https://launchpad.net/~ci-train-ppa-service/+archive/ubuntu/stable-phone-overlay