Window being maximized while holding title bar I often will hold a window's title bar while reading something, and every once in a while the window will become maximized while I'm holding it.

I can't totally reproduce this, so I'm not sure the exact behavior that's causing it. I'm not hitting any other keys while holding the window, and I believe I'm holding it still. A bit of looking on Google isn't yielding me results. I hold onto windows by habit so this has become pretty annoying.

macOS High Sierra 10.13.1
Is it possible you're double-clicking as you hold the window, whether through click input or your mouse having a hardware issue? Double-clicking a window title bar will zoom the window.

You can disable this behaviour in in System Preferences → Dock → Double-click a window's title bar to zoom.