2. When switching between high contrast and regular theming
a. The two settings from (1) are lost.
b. You can only save one theme (high contrast or regular) and the other resets to default.
These two issues make Shift+Alt+PrtScn useless. Switching is useful for web browsing, I use Edge and it applies high contrast theming to the page. This is almost always good actually, but it can make SVG graphs difficult to read (e.g. on Wikipedia), big black bars when hovering over video elements, and other small issues.