Double-clicking a window’s top or bottom border doesn’t maximize the window’s height any longer
Samsung MultiScreen (v3.0.23) that has been shipped with my latest monitors is the culprit:
MultiScreen is an available add-on software for Samsung monitors and is in no way necessary for your monitor to function.
-- http://www.samsung.com/ph/support/skp/faq/789480
I de-installed it and the maximize-height-on-double-clicking-top-or-bottom-border feature works again.