I'm fairly certain that previous versions of sigil remember the location and dimensions of a windowed screen... but maybe i'm losing my mind. For me, my workflow is mostly in a windowed mode so I can have Sigil open on one side of the screen and the reference pdf on the other. But when it comes time to run through spellcheck, I maximized the window (just to cut down, however marginally, on Page Dn presses). Unless I remember to re-window it after i finished spellchecking, the next time I go to open Sigil, it will be in maximized mode (which is only logical, since that's how it was closed), but when I go to window it, it will have forgotten dimensions and location of the last windowed mode (ie, on the right hand half the screen, fully extended top-to-bottom).
Remembering to window it after spellchecking (but before closing) is not by any stretch a gigantic inconvenience. And, really, neither is re-positioning the windowed view in the event i forget to un-maximize. Just thought I'd put it out there... heaven knows I've been trying to come up with a substantial bug/fix request, but you guys have apparently done too good a job. Curses!