1.) When user goes from a shared theme w/custom stylesheet to custom template importing the same theme, the custom stylesheet gets overwritten. It should get overwritten only if the imported theme is different than the shared theme, to allow the user to upgrade naturally from shared&custom stylesheet to custom theme using the shared theme while not losing the custom stylesheet.
2.) When user goes from custom to shared theme, the custom stylesheet is not getting obliterated as already happens when the user goes from one shared theme to a different shared theme. As a result, the custom stylesheet from the custom theme ends up being used with the shared theme, messing up the appearance of the shared theme.