I tried in 0.9.18. Removing "Show grid" check made the grid disappear, also after restarting Lazarus. Window placement seems to get lost. I guess that is broken somewhere before release of 0.9.18 (tested on Linux). The width's of the windows are preserved. However not all windows are restored.
So in short there seems to be a bug (at least in GTK widget) with regard to windows restore after a restart. 'Snap to Grid' and 'Show Grid' are working.