running PixInsight Core 01.08.04.1195 Ripley (x64) on OSX 10.11.3 (15D21), on MacBook Pro (Retina, 15 pulgadas, mediados de 2015).
When first open PI, the main window fill all the screen of the macbook. Working normally with PI, the mail window auto-grow in horizontal from the right, so you end with a bigger main PI window than the screen. You have to resize the main window to continue working comfortably with the application.
Working normally mean open an image, apply some proceses, moving the inside windows, etc. In some moment, at the same time you make some process or move a window or what ever, the main window grow!
One of the process that make main window grow is DinamicBackgroundExtraction. Seems that the toolbar gets bigger, and make the window resize.
Thanks
Joaquin.