Simile changes symbol sizes in main diagram model when creating a submodel for plug and play

There are a few factors that come together to cause this kind of problem. If your submodel is very small, then the new window will be larger than the area to be displayed (because it must initially be wide enough to show all the buttons), so Simile creates some extra scroll area to cover the extra space. This must all fit inside the submodel in the main window, so it zooms out to acomodate it all. There are several things you could do, any of these would work:

1. Make your submodel wider to start with so it does not have to be scaled to fit the new window
2. Go to edit -> preferences and turn off display of tool/component/equation bars by default in new windows. The new window will then be small if it is displaying a small submodel.
3. After opening the window, select 'View -> Zoom to fit' in it (or use the zoom-to-fit button); this will expand the submodel components to fill the wider axis of the window, and fill their whole submodel. You will have to scroll the submodel window along its narrower axis to see all the submodel contents in it.

Hope this helps!