Thanks for your reports, we've now managed to reproduce this in the office. Since update 18.104.22.168, it looks like Apple have changed something in the way they update playcounts in iTunes which is causing the scrobbler to pick them up a second time as device scrobbles. :/
Our developers are looking into this, but as others have mentioned the best workaround for the time being is to either Disable device scrobbling entirely, or to ensure that Confirm Device Scrobbles is checked -- unfortunately doing so means you have to periodically dismiss the unwanted device scrobbles.
You can adjust this setting in Preferences -> Devices.