While the window control buttons are on right it's close, maximize & minimize, but while they are on left it's close, minimize & maximize on Ubuntu 18.04 LTS. It's bothering the hell out of me. Shouldn't they be close, maximize and minimize while they are on the left side?
I think the rationale behind this is the following:
"minimise and maximise buttons should be arranged left to right and the close button should always be at the end of the title bar."
Note that both "close, minimise and maximise in left" and "minimise, maximise and close in right" follow this "rule".
(image source: an UbuntuHandbook article)
If you want the "close, maximise and minimise" order in left, then open Terminal and run the following command.
gsettings set org.gnome.desktop.wm.preferences button-layout 'close,maximize,minimize:'