System: ID version 17.4.2 on Windows 10.
Problem: some fonts have weights like "Light", next to Regular and Bold. If a text is set to weight Light and you change to Bold by Ctrl+Shift+B, the text becomes bold. When changing it back, it doesn't become Light, but Regular. The logic would be to check if there is a paragraph style applied and what's its default weight and use this when "unbolding".