My monitors are arranged like:

[1] (1440x900)

[2][3] (both 1920x1080)

My main monitor is set to [2]. Occasionally I bring a chat window down from the top monitor [1] to bottom monitor [2]. If I click the window drag bar on the top 25% of the bar and pull it down the window shrinks as I move it onto the lower monitor. The lower half of the bar doesn't have the same "feature". I don't see an option to disable this in the settings, so I am assuming it's a bug.

Clicked and held on top 25% of bar. See picture for example.

Still clicking the same spot - I have not let go.

Final window position after I left go.

Hope this is helpful / it can be fixed!